Method and apparatus for configuring a transmission mode for a backhaul link transmission

ABSTRACT

A method and a base station are described for transmitting a signal. The base station transmits control information to a relay node through a relay-physical downlink control channel (R-PDCCH), and transmits a data to the relay node through a relay-physical downlink shared channel (R-PDSCH). When a number of transmission layers of the R-PDSCH is 2 or more than 2, reference signals, among a plurality of reference signals, transmitted by a specific one of a plurality of antenna ports are used, in the relay node, for a demodulation of the control information.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of co-pending U.S. patent applicationSer. No. 13/383,804 filed on Jan. 20, 2012, which is the National Phaseof PCT/KR2010/004555 filed on Jul. 13, 2010, which claims priority under35 U.S.C. 119 to U.S. Provisional Application Nos. 61/225,206 filed onJul. 13, 2009; 61/226,285 filed on Jul. 17, 2009; 61/233,124 filed onAug. 11, 2009; and 61/236,549 filed on Aug. 25, 2009, all of which arehereby expressly incorporated by reference into the present application.

BACKGROUND OF THE INVENTION

1. Technical Field

ITU-R (International Telecommunication Union Radio communication sector)is in progress with standardization of IMT (International MobileTelecommunication)-Advanced which is a next-generation mobilecommunication system standard after third generation communicationsystems. IMT-Advanced aims to support IP (Internet Protocol)-basedmultimedia services that may provide a data rate up to 1 Gbps instationary or low-speed moving situations and a data rate up to 100 Mbpswhile moving at high speed.

2. Background Art

3GPP (3^(rd) Generation Partnership Project) prepares for LTE-Advancedthat is an advancement of LTE (Long Term Evolution) based on OFDMA(Orthogonal Frequency Division Multiple Access)/SC-FDMA (SingleCarrier-Frequency Division Multiple Access) transmission schemes assystem standards satisfying IMT-Advanced. LTE-Advanced is a leadingcandidate for IMT-Advanced. As main technologies, LTE-Advanced includesrelay station related technologies.

A relay station is a device that relays signals between a base stationand a terminal and used to expand cell coverage for a radiocommunication system and to enhance throughput of the system.

In an existing OFDM-based mobile communication system, a network hasbeen configured so that a base station is directly connected to aterminal. However, in an advanced OFDM-based mobile communicationsystem, a base station may be connected to a terminal via a relaystation. That is, relay stations relay communication between basestations and terminals by transmitting transmission upstream ordownstream transmission packets. This scheme is called “relaying”.

In a radio communication system including a relay station, a linkbetween a base station and the relay station is referred to as a“backhaul link”. A link through which the base station transmits signalsto the relay station is referred to as a “backhaul downlink”, and a linkthrough which the relay station transmits signals to the base station isreferred to as a “backhaul uplink”. There are various transmission modesthat may apply to the backhaul downlink and the backhaul uplink. Forexample, such transmission modes include a single antenna transmissionmode, which is a most basic transmission mode, a transmit diversity modeusing a plurality of antennas, a rank 1 single codeword precodingtransmission mode, a closed loop precoding based spatial multiplexingmode, and an open loop precoding based spatial multiplexing mode. Ofsuch various transmission modes, any one or more transmission modes maybe applicable to the backhaul downlink and/or backhaul uplink.

A control channel through which a base station transmits controlinformation to a relay station is called “R-PDCCH (relay-physicaldownlink control channel)”, and a data channel through which the basestation transmits data to the relay station is called “R-PDSCH (relayphysical downlink shared channel). There is a problem as to how toconfigure a transmission mode for R-PDCCH and R-PDSCH that aretransmitted on the subframe in the backhaul downlink. There is also aproblem as to how to configure reference signals that apply to decodingfor each of various transmission modes.

SUMMARY OF THE INVENTION

A method of configuring a transmission mode in a backhaul link between abase station and a relay station, a method of configuring a referencesignal applying to each transmission mode, and an apparatus for the sameare provided.

According to an aspect of the present invention, there is provided amethod of configuring a transmission mode for backhaul link transmissionin a radio communication system including a relay station, the methodcomprising transmitting a R-PDCCH (relay-physical downlink controlchannel) including backhaul control information from a base station tothe relay station and transmitting a R-PDSCH (relay-physical downlinkshared channel) including backhaul data from the base station to therelay station, wherein the R-PDCCH is transmitted in any one selectedfrom a plurality of predetermined transmission modes and wherein areference signal transmitted through the R-PDCCH for demodulation of theR-PDCCH is determined based on the selected transmission mode.

The R-PDCCH may be transmitted in S OFDM symbols (S is a natural numberbetween 1 and 6) in a backhaul downlink subframe including a pluralityof OFDM (orthogonal frequency division multiplexing) symbols in a timedomain, and the S OFDM symbols may be located after a protection sectionnecessary for a transmission/reception switching of the relay stationand OFDM symbols in the backhaul downlink subframe in which the relaystation transmits control information to a relay station terminal.

When a transmission mode for transmitting the R-PDCCH is a singleantenna transmission mode or a transmit diversity transmission modeusing a plurality of antennas, the reference signal transmitted fordemodulation of the R-PDCCH may be a reference signal commonlytransmitted from the base station in a cell.

When a transmission mode for transmitting the R-PDCCH is a singleantenna transmission mode or a transmit diversity transmission modeusing a plurality of antennas, the reference signal transmitted fordemodulation of the R-PDCCH may be a reference signal commonlytransmitted from the base station in a cell and commonly transmitted tothe relay station in the cell.

The reference signal transmitted for demodulation of the R-PDCCH may bemapped with a resource element of a fourth OFDM symbol in the backhauldownlink subframe and transmitted, or mapped with the resource elementof the fourth OFDM symbol and a resource element of a sixth OFDM symboland transmitted.

When a transmission mode for transmitting the R-PDCCH is a transmissionmode to which a precoding matrix or a precoding vector applies, thereference signal transmitted for demodulation of the R-PDCCH may usepart of the reference signal transmitted for demodulation of theR-PDSCH.

The transmission mode for transmitting the R-PDCCH may be rank 1transmission or rank 2 transmission.

When a transmission mode for transmitting the R-PDCCH is equal to thetransmission mode for transmitting the R-PDSCH, the reference signaltransmitted for demodulation of the R-PDCCH may use part of thereference signal transmitted for demodulation of the R-PDSCH.

According to another aspect of the present invention, there is provideda relay station comprising a RF unit transmitting and receiving radiosignals and a processor connected to the RF unit, wherein the processorreceives a R-PDCCH (relay-physical downlink control channel) includingbackhaul control information and a R-PDSCH (relay-physical downlinkshared channel) including backhaul data from a base station, wherein theR-PDCCH is received in any one selected from a plurality ofpredetermined transmission modes and wherein a reference signaltransmitted through the R-PDCCH for demodulation of the R-PDCCH isdetermined based on the selected transmission mode.

The R-PDCCH may be received in S OFDM symbols (S is a natural numberbetween 1 and 6) in a backhaul downlink subframe including a pluralityof OFDM (orthogonal frequency division multiplexing) symbols in a timedomain, and the S OFDM symbols may be located after a protection sectionnecessary for a transmission/reception switching of the relay stationand OFDM symbols in the backhaul downlink subframe in which the relaystation transmits control information to a relay station terminal.

Various transmission modes may apply to the backhaul link between thebase station and relay station. The transmission mode of the controlinformation transmission channel according to each transmission mode andtransmission method of the reference signal used for the correspondingtransmission mode are provided.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates a radio communication system including relaystations.

FIG. 2 exemplifies links present in a radio communication systemincluding a relay station.

FIG. 3 is a view conceptually illustrating implementations of functionalmodules in a relay station in light of implementing a device.

FIG. 4 illustrates a structure of a 3GPP LTE radio frame.

FIG. 5 illustrates an example of a resource grid for one downlink slot.

FIG. 6 illustrates a structure of a downlink subframe.

FIG. 7 illustrates a structure of an uplink subframe.

FIG. 8 illustrates an example of a transmitter and a receiver in whichmultiple MACs operate multiple carriers.

FIG. 9 illustrates a transmitter and a receiver in which one MACoperates multiple carriers.

FIG. 10 illustrates an example of a backhaul downlink subframe.

FIG. 11 illustrates an example of semi-statically allocating andconfiguring the R-PDCCH transmission resources.

FIG. 12 illustrates an example of dynamically allocating and configuringthe R-PDCCH transmission resources.

FIG. 13 illustrates another example of the method of dynamicallyallocating and configuring the R-PDCCH transmission resources.

FIG. 14 illustrates another example of the method of dynamicallyallocating and configuring the R-PDCCH transmission resources.

FIG. 15 illustrates still another example of the method of dynamicallyallocating and configuring the R-PDCCH transmission resources.

FIG. 16 illustrates an example of dynamically or semi-staticallyallocating and configuring the R-PDCCH transmission resources.

FIG. 17 illustrates another example of dynamically or semi-staticallyallocating and configuring the R-PDCCH transmission resources.

FIG. 18 illustrates an example of allocating cell-specific and relaystation-common reference signal patterns to an area in which the R-PDCCHis transmitted in the backhaul downlink subframe.

FIG. 19 illustrates an example of a cell specific reference signal forfour antenna ports in the subframe to which the normal CP applies.

FIG. 20 illustrates an example of a cell specific reference signal forfour antenna ports in the subframe to which the extended CP applies.

FIGS. 21 to 23 illustrate examples of backhaul downlink subframestructures that do not provide backward compatibility.

FIGS. 24 to 26 illustrate new cell specific and relay station commonreference signals (simply referred to as “new reference signals”) thatmay be used as the R-PDCCH reference signals.

FIG. 27 illustrates an example of applying two CDM groups and the OCCapplied for each CDM group.

FIG. 28 is a block diagram illustrating a radio communication systemimplementing the embodiments of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

The below-described technologies may be used for various radiocommunication systems, such as communication systems based on CDMA (codedivision multiple access), FDMA (frequency division multiple access),TDMA (time division multiple access), OFDMA (orthogonal frequencydivision multiple access), SC-FDMA (single carrier frequency divisionmultiple access). CDMA may be implemented as a radio technology such asUTRA (Universal Terrestrial Radio Access) or CDMA2000. TDMA may beimplemented as radio technologies such as GSM (Global System for Mobilecommunication)/GPRA (General Packet Radio Service)/EDGE (Enhanced DataRates for GSM Evolution). OFDMA may be implemented as radio technologiessuch as IEEE 802.11 (Wi-Fi), IEEE 802.16e (WiMAX), IEEE 802-20, E-UTRA(Evolved UTRA). UTRA is part of UMTS (Universal MobileTelecommunications System). 3GPP (3rd Generation Partnership Project)LTE (long term evolution) is part of E-UMTS (Evolved UMTS) using E-UTRAand adopts OFDMA for downlink and SC-FDMA for uplink. LTE-Advanced(LTE-A) is an advanced version of LTE. For clarity, 3GPP LTE/LTE-A isdescribed as an example, but the present invention is not limitedthereto.

FIG. 1 illustrates a radio communication system including relaystations.

Referring to FIG. 1, the radio communication system 10 including relaystations includes at least one base station 11 (eNodeB, eNB). Each basestation 11 provides communication services in a specific geographicalarea 15 which is generally called a “cell”. The cell may be divided intomultiple subareas each of which is called a “sector”. One base stationmay include one or more cells. The base station 11 refers to a fixedstation communicating with a terminal 13 and may have various names,such as BS (Base Station), BTS (Base Transceiver System), AP (AccessPoint), or AN (Access Network). The base station 11 may performfunctions such as connectivity, management, control, and resourceallocation between a relay station 12 and a terminal 14.

The relay station 12 (Relay Node, RN) is a device relaying signalsbetween the base station 11 and the terminal 14, and may have differentnames, such as RS (Relay Station), repeater, or relay. The relay station12 may adopt various relay schemes, such as, but not limited to, AF(amplify and forward) and DF (decode and forward).

The terminals 13 and 14 (User Equipment, UE) may be stationary or mobileand may have various names, such as MS (Mobile Station), UT (UserTerminal), SS (Subscriber Station), wireless device, PDA (PersonalDigital Assistant), wireless model, handheld device, or AT (AccessTerminal). Hereinafter, a macro terminal (macro UE, Ma-UE, 13) refers toa terminal directly communicating with the base station 11, and a relayterminal (RN-UE, 14) refers to a terminal communicating with the relaystation. Although in the cell of the base station 11, the macro terminal13 may communicate with the base station 11 via the relay station 12 toenhance transmission rate based on diversity effects.

FIG. 2 exemplifies links present in a radio communication systemincluding a relay station.

When a relay station is located between a base station and a terminal, alink may differ from a link in a radio communication system includingonly base station(s) and terminal(s). A downlink and an uplink betweenthe base station and terminal, respectively, refer to a communicationlink from the base station to the terminal and a communication link fromthe terminal to the base station. In the case of adopting TDD (TimeDivision Duplex), downlink transmission and uplink transmission areperformed at different subframes. In the case of adopting FDD (FrequencyDivision Duplex), downlink transmission and uplink transmission areperformed at different frequency bands. In TDD, downlink transmissionand uplink transmission are performed at different times and may use thesame frequency band. On the contrary, in FDD, downlink transmission anduplink transmission may be performed at the same time of period but usedifferent frequency bands.

In addition to the above-described uplink and downlink, in the case thata relay station is included between the base station and the terminal,backhaul links and access links may be provided. The backhaul linksrefer to communication links between the base station and the relaystation, and include a backhaul downlink through which the base stationtransmits signals to the relay station and a backhaul uplink throughwhich the relay station transmits signals to the base station. Theaccess links refer to communication links between the relay station anda terminal connected to the relay station—this terminal is referred toas a “relay station terminal,” and include an access downlink throughwhich the relay station transmits signals to the relay station terminaland an access uplink through which the relay station terminal transmitssignals to the relay station.

In the backhaul downlink and access downlink, 1) in case of TDD,transmission may be performed at the same time resources as thedownlink, that is, at the subframes, and 2) in case of FDD, transmissionmay be performed at the same frequency resources as the downlink, thatis, at the frequency bands. In the backhaul uplink and access uplink, 1)in case of TDD, transmission may be performed at the same time resourcesas the uplink, that is, at the subframes, and 2) in case of FDD,transmission may be performed at the same frequency resources as theuplink, that is, at the frequency bands.

In other words, the base station may have a receiving module (atransmitting module in case of the terminal) for the uplink and atransmitting module (a receiving module in case of the terminal) for thedownlink. On the contrary, the relay station should have a transmittingmodule for the backhaul uplink adopting the same radio resources as theuplink and a receiving module for the access uplink. Further, the relaystation should have a receiving module for the backhaul downlinkadopting the same radio resources as the downlink and a transmittingmodule for the access downlink. This can be represented as in thefollowing table:

TABLE 1 Functionality eNodeB Relay node UE DL TX 0 0 DL RX 0 0 UL TX 0 0UL RX 0 0

FIG. 3 is a view conceptually illustrating implementations of functionalmodules in a relay station in light of implementing a device.

Referring to FIG. 3, a relay station should be able to receive signalsfrom a base station in a backhaul downlink and perform OFDMA signalprocess via FFT (Fast Fourier Transform). The relay station should alsobe able to receive signals from a relay station terminal in an accessuplink and perform OFDMA signal process through FFT. The above twoprocedures may be performed at the same time.

The relay station should be able to transmit signals to the base stationafter performing DFT-s-OFDMA (SC-FDMA) signal process in the backhauluplink. The relay station should also be able to transmit signals to therelay station terminal after performing DFT-s-OFDMA (SC-FDMA) signalprocess in the access downlink. The above two procedures may besimultaneously performed.

However, it is assumed to be difficult for the relay station to receivesignals from the relay station terminal in the access uplink whilesimultaneously transmitting signals to the base station in the backhauluplink. It is also assumed that it is difficult for the relay station toreceive signals from the base station in the backhaul downlink whilesimultaneously transmitting signals to the relay station terminal in theaccess downlink.

If a duplexer is implemented in both directions, IFFT and base bandmodule line associated with transmission/reception over a certaincarrier frequency band may be represented as being split.

FIG. 4 illustrates a structure of a 3GPP LTE radio frame.

Referring to FIG. 4, a radio frame includes ten subframes each of whichincludes two slots. The length of each subframe may be 1 ms and thelength of each slot may be 0.5 ms. Time taken for one subframe to betransmitted is referred to as a TTI (Transmission Time Interval). TTImay be a minimum unit for scheduling.

One slot may include a plurality of OFDM (Orthogonal Frequency DivisionMultiplexing) symbols in a time region. The OFDM symbol uses OFDMA fordownlink in case of 3GPP LTE, and thus, may be called another name torepresent a symbol period. For instance, in the case that SC-FDMA isused for uplink multiple access, it can be referred to as SC-FDMAsymbol. Although it is described as an example that one slot includesseven OFDM symbols, the number of OFDM symbols included in one slot mayvary according to the length of CP (Cyclic Prefix). According to 3GPP TS36.211 V8.5.0 (2008-12), for normal CP, one subframe includes seven OFDMsymbols and for extended CP, one subframe includes six OFDM symbols. Theradio frame structure is merely an example, and the number of thesubframes included in the radio frame and the number of slots includedin the subframe may change. Hereinafter, the symbol may denote one OFDMsymbol or one SC-FDMA symbol.

For the radio frame structure described in connection with FIG. 4, referto section.4.1 and section.4.2 of 3GPP TS 36.211 V8.3.0 (2008-05)“Technical Specification Group Radio Access Network; Evolved UniversalTerrestrial Radio Access (E-UTRA); Physical Channels and Modulation(Release 8)”.

FIG. 5 illustrates an example of a resource grid for one downlink slot.

In a radio frame used for FDD or TDD, one slot includes plural OFDMsymbols in the time domain and plural resource blocks (RBs) in thefrequency domain. The resource block includes a plurality of consecutivesubcarriers in one slot as a resource allocation unit.

Referring to FIG. 5, one downlink slot includes seven OFDM symbols andone resource block includes twelve subcarriers in the frequency domain.However, the present invention is not limited thereto. The subcarriersin the resource block may have an interval of, e.g., 15 KHz.

Each element on the resource grid is called “resource element” and oneresource block includes 12×7 resource elements. The number (NDL) ofresource blocks included in the downlink slot depends upon a downlinktransmission bandwidth set in a cell. The resource grid described inconnection with FIG. 5 may apply to the uplink as well.

FIG. 6 illustrates a structure of a downlink subframe.

Referring to FIG. 6, a subframe includes two consecutive slots. Firstthree OFDM symbols in the first slot of the subframe correspond to acontrol region to which a PDCCH (Physical Downlink Control Channel) isallocated and the other OFDM symbols correspond to a data region towhich a PDSCH (Physical Downlink Shared Channel) is allocated. Besidesthe PDCCH, control channels, such as PCFICH (physical control formatindicator channel), PHICH (physical HARQ indicator channel), etc., maybe allocated in the control region. The terminal may decode controlinformation transmitted through the PDCCH and may read data informationtransmitted through the PDSCH. Here, the control region including threeOFDM symbols is merely an example, and the control region may includetwo OFDM symbols or a single OFDM symbol. The number of OFDM symbolsincluded in the control region of the subframe may be known through thePCFICH which carries information on whether it is successful to receiveuplink data transmitted from the terminal.

The control region includes a logical CCE column which includes pluralCCEs (Control Channel Elements). The CCE column is a set of the wholeCCEs constituting the control region in one subframe. The CCEscorrespond to the plurality of resource element groups (REGs). Forinstance, the CCEs may correspond to nine REGs. The REG is used todefine mapping the control channel with the resource elements. Forinstance, one REG may include four resource elements.

Plural PDCCHs may be transmitted in the control region. The PDCCHcarries control information, e.g., associated with schedulingallocation. The PDCCH is transmitted onto a single or an aggregation ofa few consecutive CCEs. The format of the PDCCH and the number of bitsavailable for the PDCCH are determined based on the number of CCEsconstituting the CCE aggregation. The number of CCEs used fortransmission of the PDCCH is referred to as a “CCE aggregation level”which is a CCE unit for searching the PDCCH. The size of the CCEaggregation level is defined as the number of adjacent CCEs. Forinstance, the CCE aggregation level may be an element in a set {1, 2, 4,8}.

Control information transmitted through the PDCCH is referred to as“downlink control information (DCI)”. The DCI includes uplink schedulinginformation, downlink scheduling information, system information, uplinkpower control command, control information for paging, and controlinformation used for instructing random access response (RACH response).

The DCI format includes format 0 for PUSCH (Physical Uplink SharedChannel) scheduling, format 1 for scheduling of a single PDSCH (PhysicalDownlink Shared Channel) codeword, format 1A for compact scheduling of asingle PDSCH codeword, format 1B for compact scheduling for rank-1transmission of a single codeword in a spatial multiplexing mode, format1C for very compact scheduling of DL-SCH (Downlink Shared Channel),format 1D for PDSCH scheduling in a multiple user spatial multiplexingmode, format 2 for PDSCH scheduling in a closed-loop spatialmultiplexing mode, format 2A for PDSCH scheduling in an open-loopspatial multiplexing mode, format 3 for transmission of TPC(Transmission Power Control) commands for two bit power control forPUCCH and PUSCH, and format 3A for transmission of TPC commands for onebit power control for PUCCH and PUSCH.

FIG. 7 illustrates a structure of an uplink subframe.

Referring to FIG. 7, the uplink subframe may include a control region towhich a PUCCH (Physical Uplink Control Channel) is allocated to carryuplink control information in the frequency domain and a data region towhich a PUSCH (Physical Uplink Shared Channel) is allocated to carryuser data.

The PUCCH for a single terminal is allocated in a pair of RBs 51 and 52in the subframe and the RBs 51 and 52 in the RB pair occupies differentsubcarriers in two slots, respectively. This is represented as “the RBpair allocated in the PUCCH is subjected to frequency hopping at a slotboundary”.

The PUCCH may support multiple formats. That is, the PUCCH may transmituplink control information having a different number of bits per framedepending on a modulating scheme. For example, in the case of using BPSK(Binary Phase Shift Keying) (PUCCH format 1a), one bit uplink controlinformation may be transmitted over the PUCCH, and in the case of usingQPSK (Quadrature Phase Shift Keying) (PUCCH format 1b), two bit uplinkcontrol information may be transmitted over the PUCCH. Other PUCCHformats include format 1, format 2, format 2a, and format 2b (fordetails, see section. 5.4 in 3GPP TS 36.211 V8.2.0 (2008-03) “TechnicalSpecification Group Radio Access Network; Evolved Universal TerrestrialRadio Access (E-UTRA); Physical Channels and Modulation (Release 8)”).

[Construction and Configuration of Carrier Aggregation]

A 3GPP release 8 (release 9 may be also included, hereinafter referredto as “3GPP LTE”) system supports transmission/reception in a singlecarrier state that includes a scalable frequency band. That is, the 3GPPLTE system is a single carrier system that supports only a singlebandwidth (that is, a single component carrier (CC)) among 1.4, 3, 5,10, 15, and 20 MHz. For instance, the 3GPP LTE system supports up to 20MHz and may have different uplink and downlink bandwidths. However, the3GPP LTE system supports only one CC for the uplink and downlink.

On the contrary, a 3GPP LTE-A system uses multiple carriers (CCs) andsupports carrier aggregation. The carrier aggregation (also referred toas “spectrum aggregation” or “bandwidth aggregation”) supports widebandaggregated carriers by combining narrowband carriers. The carrieraggregation has been introduced to support growing throughput, preventan increase in expenses due to adoption of wideband RF (Radio Frequency)elements, and guarantee comparability with existing systems. Forexample, if five CCs are allocated as granularity of a carrier unithaving 20 MHz bandwidth, up to 100 MHz of bandwidth may be supported.

The size of CC (or the bandwidth of CC) may vary. For example, when fiveCCs are used to configure 70 MHz bandwidth, the configuration may be asfollows: 5 MHz carrier (CC #0)+20 MHz carrier (CC #1)+20 MHz carrier (CC#2)+20 MHz carrier (CC #3)+5 MHz carrier (CC #4).

A situation where the number of downlink CCs is equal to the number ofuplink CCs or the bandwidth of the downlink is equal to the bandwidth ofthe uplink is referred to as “symmetric aggregation”. A situation wherethe number of downlink CCs is different from the number of uplink CCs orthe bandwidth of the downlink is different from the bandwidth of theuplink is referred to as “asymmetric aggregation”

In a radio communication system supporting carrier aggregation, a cellor base station may perform downlink transmission to a terminal in thesame time resource (for example, the subframe) using frequency resources(for example, subcarriers or resource blocks) over one or more carriers.Likewise, the terminal may perform uplink transmission to the cell orbase station in the same time resource (for example, the subframe) usingfrequency resources (for example, subcarriers or resource blocks) overone or more carriers.

In the multiple carrier system, at least one or more MAC (Medium AccessControl) entities may conduct transmission and reception bymanaging/operating at least one or more CCs. The MAC entity has a layerhigher than the physical layer (PHY). For example, the MAC entity mayhave an MAC layer and/or its upper layer.

FIG. 8 illustrates an example of a transmitter and a receiver in whichmultiple MACs operate multiple carriers. (A) of FIG. 8 illustrates thetransmitter and (B) of FIG. 8 illustrates the receiver. The multipleMACs (MAC 0, . . . , MAC n−1) are mapped to multiple physical layers(PHY 0, . . . , PHY n−1) in a one-to-one correspondence. Each CC has anindependent physical layer and an independent MAC layer. The MAC layerof the transmitter performs L1/L2 scheduling for the MAC/RLC (Radio LinkControl) layer and generation of MAC PDU (Protocol Data Unit). The MACPDU generated in the MAC layer of the transmitter is converted into thetransport block through the transport channel and then mapped to thephysical layer.

FIG. 9 illustrates a transmitter and a receiver in which one MACoperates multiple carriers. (A) and (B) of FIG. 9 illustrate thetransmitter and the receiver, respectively. One physical layer (PHY)corresponds to one CC and multiple physical layers (PHY 0, . . . , PHYn−1) are operated by one MAC. The MAC may be mapped to the multiplephysical layers (PHY 0, . . . , PHY n−1) dynamically or statically. TheMAC PDU generated in the MAC layer of the transmitter is converted intothe transport block through the transmission channel, decomposed, andthen mapped to the physical layer.

In the radio communication system including the relay station, the relaystation performs communication in the backhaul uplink/downlink and theaccess uplink/downlink, and relays signals between the base station andthe terminal. The relay station may be classified into a few types as inTable 2 according to its functions:

TABLE 2 L1 Relay L2 Relay L3 Relay (Type-3 (Type-2 (Type-1 functionrelay) relay) relay) RF function ◯ ◯ ◯ Coder/Decoder and CRC — ◯ ◯ HARQ— ◯ ◯ Multiplex & Demultiplex of — ◯ ◯ MAC SDU Priority(Qos) handling —◯ ◯ Scheduling — ◯ ◯ Outer ARQ — (◯) ◯ (Re)-Segmentation and — (◯) ◯concatenation Header compression(ROHC) — — — Reordering of lower layerSDUs — — — In-sequence delivery of upper layer — — — PDUs Duplicatedetection of lower — — — layer SDUs Ciphering — — — System informationbroadcast — — ◯ RRC Connection set-up and — — ◯ maintenance RadioBearers set-up and — — — maintenance Mobility function — — ◯ MBMSservices control — — — Paging — — — QoS management — — (◯) UEmeasurement reporting and — — (◯) control the reporting NAS signallinghandling — — —

In Table 2, ‘O’ means that the corresponding function is supported,‘(O)’ that the corresponding function may be supported, and ‘-’ that thecorresponding function is not supported. The L1 relay station has a fewadditional functions as well as an AF (Amplify and Forward) function,which amplifies signals from the base station or terminal and thenforwards the amplified signals to the terminal or base station. That is,the L1 relay station refers to a relay station that cannot perform anindependent scheduling function and may be merely regarded as arepeater. The L2 relay station has a scheduling function together with aDF (Decoding and Forward) function, which restores information throughprocedures, e.g., by demodulating and decoding signals from the basestation or terminal and then generates signals through procedures suchas coding and modulation, then forwards the generated signals to theterminal or base station. The L3 relay station (type 1 relay station) issimilar to one cell and in addition to functions owned by the L2 relaystation, may support call connection and mobility functions. AlthoughTable 2 classifies the relay stations into the L1 relay station (type 3relay station), L2 relay station (type 2 relay station), and L3 relaystation (type 1 relay station), the present invention is not limitedthereto. Such classification is made depending on schematiccharacteristics of the L1, L2, and L3 relay stations, and does notcompletely comply with the terms. Hereinafter, type 1 relay stationmeans a relay station that has the same functions as the base station(Hereinafter, “cell” is assumed to have the same meaning as the basestation and that may include independent RRM (Radio Resource Management)and L1/L2 layers and may have a physical cell ID.

FIG. 10 illustrates an example of a backhaul downlink subframe.

The backhaul downlink subframe may be divided in the time domain into anaccess signal transmission section, a protection section, and a backhaulreceiving section.

The access signal transmission section includes first N (N is one of 1,2, and 3) OFDM symbols of the subframe and may be used to transmitaccess downlink signals to the relay station terminal. The relay stationtransmits the access downlink signals to the relay station terminal inorder to support signal measuring functions of the relay stationterminal, especially legacy terminals that operate based on LTE release8/9. The relay station may notify the legacy terminals through theaccess downlink signals that the subframe is used for signal receptionof the base station. It is difficult for the relay station to receivesignals from the base station due to self interference in the accesssignal transmission section.

The protection section is a time period for stabilization according tosignal transmission/reception switching of the relay station and may beequal to or shorter than the length of one OFDM symbol, or as the casemay be, may be longer than the length of one OFDM symbol. The protectionsection may be set as a time period in the time domain or may be set asa time sample value. Although two protection sections 301 and 302located before and after the backhaul receiving section are shown inFIG. 10, the present invention is not limited thereto. That is, theprotection section 302 located after the backhaul receiving section maybe not provided when the backhaul downlink subframe is consecutively setor depending on timing alignment relation of the subframe. In this case,the backhaul receiving section may be extended up to the last OFDMsymbol of the subframe. The protection section may be defined only for afrequency band set in order for the base station to transmit signals tothe relay station over any downlink component carrier (DL CC).

During the backhaul receiving section, the relay station may receivesignals from the base station in the downlink subframe. The backhaulreceiving section may include, in the backhaul downlink subframe, all orsome of the OFDM symbols except for the access signal transmissionsection and the protection section.

The OFDM symbols included in the backhaul receiving section and theaccess signal transmission section may be independently applied with anormal CP or extended CP.

For convenience of description, resources constituted of backhaulreceiving sections in the time domain and bands allocated to the relaystation in the frequency domain are referred to as a “backhaul receivingarea”. In the backhaul receiving area, R-PDCCH (relay-physical downlinkcontrol channel) and R-PDSCH (relay-physical downlink shared channel)are transmitted by the base station. As the case may be, R-PCFICH(relay-physical control format indicator channel) and/or R-PHICH(relay-physical HARQ indicator channel) may be additionally transmitted.The R-PDCCH is a control channel in which the base station transmitscontrol information to the relay station, and the R-PDSCH is a datachannel in which the base station transmits data to the relay station.The R-PCFICH is a channel transmitting information on the number of theOFDM symbols or the frequency band, and the R-PHICH is a channeltransmitting HARQ ACK/NACK of the base station in response to thetransmission of the backhaul uplink data by the relay station.Hereinafter, the x area refers to a radio resource area in which x istransmitted. For example, the R-PDCCH area means a radio resource areain which the R-PDCCH is transmitted by the base station.

In the case that the R-PDCCH and the R-PDSCH (if defined, R-PCFICHand/or R-PHICH are also included hereinafter) are mapped with physicalresources and transmitted, various transmission modes may be presentthat apply to these channels. The definition and application method ofreference signals RSs used for demodulation or decoding of the relaystation depending on what transmission mode is to apply among thevarious transmission modes are hereinafter described.

FIG. 11 illustrates an example of semi-statically allocating andconfiguring the R-PDCCH transmission resources.

In the backhaul downlink, traffics are not likely to highly changebecause the terminal which is subjected to statistical multiplexing withthe relay station varies with time. Accordingly, one way to supportallocation of radio resources in the backhaul downlink is to previouslydefine the size of backhaul resources allocated to the relay station andnot to change the backhaul resources for a long time. That is, the wayis to semi-statically allocate the backhaul resources. Such resourceallocation method preferably fixes the transmission format of thebackhaul link. The backhaul resources predefined in the backhauldownlink subframe are semi-statically scheduled and may be set orallocated through an upper level signal, such as RRC (Radio ResourceControl).

In the predetermined backhaul resources, a control channel carryingL1/L2 control information such as HARQ ACK/NACK, CQI/PMI, or schedulinggrant may be multiplexed with the backhaul data in the TDM (TimeDivision Multiplexing), FDM (Frequency Division Multiplexing), orTDM/FDM process.

When multiplexed in the TDM scheme, an area 401 to which the controlchannel is allocated is distinguished from an area to which data isallocated in the time domain. When multiplexed in the FDM scheme, anarea 402 to which the control channel is allocated is distinguished fromthe area to which data is allocated in the frequency domain. Whenmultiplexed in the TDM/FDM process, an area 403 to which the controlchannel is allocated is distinguished from an area to which data isallocated in the time and frequency domains.

The control information may be piggybacked to the backhaul data andsubjected to coding/modulation, then transmitted.

The semi-static backhaul resource allocation method may reduce theamount of control information and load to scheduling of the base stationscheduler. However, this method needs to be careful of management of thebackhaul resources and of how to restore errors that might be happening.

FIG. 12 illustrates an example of dynamically allocating and configuringthe R-PDCCH transmission resources.

A method for minimizing an influence on the macro terminal uponallocation of transmission resources is to allocate one or more resourceblocks in the PDSCH and transmit the R-PDCCH. In other words, the methodis that the R-PDCCH is multiplexed with the backhaul data for the relaystation in the frequency domain and transmitted (that is, FDM).Multiplexing the R-PDCCH and the backhaul data in the frequency domainallows resource allocation for the R-PDCCH to be simplified with noinfluence upon the macro terminal. Further, no special limit applies tothe scheduling of the base station in the backhaul and access links andflexibility is maximally guaranteed. However, the FDM method may cause adelay while the relay station decodes the backhaul data. This is why therelay station should receive the R-PDCCH from the whole backhauldownlink subframes in order to start decoding the backhaul data.

FIG. 13 illustrates another example of the method of dynamicallyallocating and configuring the R-PDCCH transmission resources.

There may be a method by which multiplexing is performed in the timedomain and an area where the backhaul data is transmitted in order toallocate the R-PDCCH transmission resources as shown in FIG. 13. Thebase station may previously define a backhaul downlink resourceallocated to the relay station, which may be called a “relay zone”, andmay transmit the backhaul downlink control information and data in therelay zone. In the relay zone, the R-PDCCH and the backhaul data aremultiplexed in the time domain. This is the same as the way the existingPDCCH and PDSCH are multiplexed in the time domain. The relay zone fortransmission of the R-PDCCH and the backhaul data may be setsemi-statically by an upper level signal. In this case, it may bepossible to obtain a frequency diversity effect by spreading in thefrequency domain an area where the R-PDCCH is transmitted. That is, theR-PDCCH may be transmitted at a larger frequency band than a frequencyband at which the R-PDSCH is transmitted. Further, since the R-PDCCH ispositioned in the time domain earlier than the area where the backhauldata is transmitted, the decoding may be conducted quickly compared tothe FDM method by which the R-PDSSCH should be received from the entiresubframes so as to decode the backhaul data. However, such a feature assemi-statically sets the relay zone may limit the scheduling flexibilityof the base station and efficient use of the radio resources.

FIG. 14 illustrates another example of the method of dynamicallyallocating and configuring the R-PDCCH transmission resources.

The R-PDCCH transmission resources may be dynamically allocated. Thedynamic resource allocation may reduce limitation to flexibility andimprove a frequency selective scheduling gain. For example, it may bepossible to split the whole system band into plural partitions andallocate some of the partitions to the relay station. The partitions maybe configured as groups of resource blocks.

The partitions may be used for PDSCH transmission for the macro terminalor may be used for backhaul transmission for the relay station. When thepartitions are used for backhaul transmission for the relay station, theR-PDCCH and the backhaul data in the partitions may be multiplexed inthe time domain. The base station may dynamically allocate the relayzone by adjusting the number of the partitions allocated for backhaultransmission of the relay station. This method may increase thefrequency selective scheduling gain over the method of semi-staticallyallocating the relay zone. The relay station may be aware of whichpartition is used for the relay zone by receiving a signal from the basestation. For instance, the base station may notify whether eachpartition is used for the relay zone by performing signaling in the formof bitmap. Or the relay station may find a relay zone allocated theretoby performing blind decoding on each partition.

FIG. 15 illustrates still another example of the method of dynamicallyallocating and configuring the R-PDCCH transmission resources (FDM/TDM).

The base station may divide the backhaul downlink resources into twotypes when allocating the backhaul downlink resources to the relaystation. One type is a predetermined resource area predefined for eachrelay station as primary backhaul resources PBRs. The primary backhaulresources may be minimally allocated. The primary backhaul resources maybe allocated to a frequency band which has the best channel state toeach relay station and may be changed by an upper level signal. In theprimary backhaul resources, a relay station-specific control channel(CCH) is transmitted which may include resource allocation informationon the backhaul data transmission band positioned in not only the samefrequency band but also a different frequency band. The control channeland backhaul data in the primary backhaul resources are multiplexed inthe time domain (TDM).

Another type includes secondary backhaul resources (SBRs). The secondarybackhaul resources may be dynamically allocated depending on traffic ofthe backhaul link. As described above, the relay station-specificcontrol channel included in the primary backhaul resources may resourceallocation information on the backhaul data transmission area includedin the secondary backhaul resources.

Such a method may apply when in the backhaul link the channel stateslowly changes. Or this method eliminates the need for the relay stationto find out the R-PDCCH over the entire frequency band in the relay zoneand the need of searching for the control channel by blind decodingbecause of receiving information on the primary backhaul resources andcontrol channel through the upper level signal.

FIG. 16 illustrates an example of dynamically or semi-staticallyallocating and configuring the R-PDCCH transmission resources.

For allocating the backhaul downlink resources to the relay station, thebase station may distinguish the backhaul downlink resources into twotypes. One type includes primary backhaul resources (PBRs) whichcorrespond to a resource area allocated to each relay station in asemi-static or dynamic manner. The relay station-specific R-PDCCH istransmitted to the first one or more OFDM symbols in the primarybackhaul resources. OFDM symbols subsequent to OFDM symbols to which theR-PDCCH is allocated are used for R-PDSCH transmission.

In the case that a channel between the base station and the relaystation changes slowly, the primary backhaul resources may be allocatedin a semi-static manner. In such case, the PBR is semi-staticallyallocated by an upper level signal and may obtain a dependent schedulinggain and low search complexity of the R-PDCCH. On the contrary, in thecase that the channel condition is unstable and changes fast, theprimary backhaul resources may be allocated in a dynamic manner. In suchcase, the relay station may search the PBR through blind decoding.Because not being able to the location of the allocated PBR, the relaystation performs search on the PBR in a predetermined search space. Inthe case of dynamically allocating the primary backhaul resources, thebase station may perform the PDSCH transmission scheduling on the macroterminal with the maximum flexibility. The primary backhaul resourcesmay be allocated for each relay station to the frequency band (resourceblocks) having the best channel condition.

The other type includes secondary backhaul resources (SBRs). Thesecondary backhaul resources may be additionally allocated depending ontraffic of the backhaul link. The R-PDSCH may be transmitted in thesecondary backhaul resources. The secondary backhaul resources may beindicated by the R-PDCCH located in the primary backhaul resources.

FIG. 17 illustrates another example of dynamically or semi-staticallyallocating and configuring the R-PDCCH transmission resources.

For allocating the backhaul downlink resources to the relay station, thebase station may distinguish the backhaul downlink resources into twotypes. One type includes primary backhaul resources (PBRs) which areallocated to each relay station in a dynamic or semi-static manner. Inthe primary backhaul resources, the R-PDCCH may be transmitted with avarying start location on the contrary to that shown in FIG. 16. Forexample, the R-PDCCH may be transmitted in the first one or morepredetermined numbers of OFDM symbols of the primary backhaul resourcesbut at a different OFDM location. As such, the fact that the startlocation of the R-PDCCH in the primary backhaul resources varies differsfrom the example described in connection with FIG. 16. OFDM symbolssubsequent to OFDM symbols to which the R-PDCCH is allocated are usedfor R-PDSCH transmission and OFDM symbols that come before the OFDMsymbols to which the R-PDCCH is allocated are used for transmission ofthe PDSCH for the macro terminal.

In the case that a channel between the base station and the relaystation changes slow, the primary backhaul resources may be allocated ina semi-static manner. In such case, the PBR may be semi-staticallyallocated by an upper level signal and obtain a channel-dependentscheduling gain and reduce search complexity of the R-PDCCH. On thecontrary, in the case that the channel characteristics are not stableand change fast, the primary backhaul resources may be allocated in adynamic manner. In such case, the relay station may search the PBRthrough blind decoding. Because of not being able to the location of theallocated PBR, the relay station searches the PBR in a predeterminedsearch space (PRB for transmission of the R-PDCCH semi-statically set).In the case that the base station dynamically allocates the frequencyselective PBR, the related R-PDSCH may be allocated to the same PBR. Inthe case that the base station dynamically allocates the primarybackhaul resources, the base station may perform PPDSCH transmissionscheduling for the macro terminal with the maximum flexibility. Theprimary backhaul resources may be allocated for each relay station to afrequency band (resource blocks) having the best channel condition.

The other type includes the secondary backhaul resources (SBRs). Thesecondary backhaul resources may be additionally allocated depending ontraffic of the backhaul link. In the secondary backhaul resources, theR-PDSCH may be transmitted. The secondary backhaul resources may beindicated by the R-PDCCH located in the primary backhaul resources.

The backhaul resource allocation methods described in connection withFIGS. 11 to 17 describe transmission resource allocation mainly for theR-PDCCH and R-PDSCH. In such backhaul resource allocation methods,transmission resource allocation of the R-PCFICH and R-PHICH may beperformed in the R-PDCCH transmission resources or R-PDSCH transmissionresources. Hereinafter, if otherwise stated, methods of settingtransmission modes for the R-PCFICH and R-PHICH and applying referencesignals used for demodulation/decoding based on the set transmissionmodes may be defined in the same way as those that have applied to theR-PDCCH.

Various transmission modes may apply to the backhaul downlink (orbackhaul uplink). For instance, the transmission modes may include asingle antenna transmission mode, a transmit diversity based on pluralantennas, a rank 1 single codeword precoding transmission, closed loopprecoding base space multiplexing, or open loop precoding base spacemultiplexing. One or more of the transmission modes may apply to thebackhaul downlink depending on the channel. The transmit diversity is atransmission mode that increases reliability by transmitting the samedata through plural transmission antennas. The space multiplexing is atransmission mode that may perform high rate data transmission withoutincreasing the bandwidth of the system by transmitting different datathrough plural transmission antennas. The closed loop precoding is atransmission mode in which the base station determines the precodingvector/matrix using channel information (e.g., PMI) fed back from thereceiving terminal, and the open loop precoding is a transmission modein which the base station determines the precoding vector/matrix withoutrespect to channel information fed back from the receiving terminal.

In the case that the base station transmits the R-PDCCH, transmissionmodes applicable to the R-PDCCH and methods of applying referencesignals applicable to demodulation and decoding of the R-PDCCH are asfollows. At this time, the transmission modes of the R-PDSCH and themethods of applying the reference signals are the same as the methodsapplying to the R-PDCCH or may be defined by rank values (i.e., thenumber of transmission layers or the number of transmission streams)configured by the relay station-specific RRC signaling and the precodingvector/matrix. Likewise, the transmission mode of the R-PDCCH andmethods of applying the reference signals and their related rank valuesand designation of the precoding vector/matrix may be configured to beperformed by the base station based on the relay station-specific RRCsignaling.

TABLE 3 R-PDCCH transmission Reference signal for Detailed Case modedemodulation/decoding characteristics Case-0 Single antenna Cellspecific RS (CRS) transmission or transmit conventionally defined indiversity using M LTE release 8/9 (M transmission antenna antenna portsin backhaul ports (M = 1, 2, or 4) link) Case-1 Single antenna New cellspecific and transmission or transmit relay station common RS diversityusing M (M antenna ports may be transmission antenna defined in givenOFDM ports (M = 1, 2, 4 or 8) symbol area) Case-2 Precoded transmit Rprecoded (virtualized) Applied precoder diversity using R virtual relaystation specific may be preset or antenna ports (R = 1, 2, or DM-RSpatterns predefined by 4) RRC signal or L1/L2 control signal signalingCase-3 Rank 1 closed loop Case-3.1: New cell precoding based specificand relay station transmission using M common RS (M antenna transmissionantenna ports may be defined in ports (M = 2, 4, or 8) given OFDM symbolarea) Case-3.2: Cell specific RS (CRS) conventionally defined in LTErelease 8/9 (M antenna ports in backhaul link) Case-4 Rank 1 closed looplayer #P pattern precoded Applied precoded precoding based DM-RS forR-PDSCH DM_RS layer transmission using M demodulation (P = 0, 1, 2,pattern may use transmission antenna 3, 4, 5, 6, 7, or 8; e.g. the sameprecoder ports (M = 2, 4, or 8) P = 0 or 1) as precoder used for R-PDCCHtransmission Case-5 Rank 1 open loop Case-5.1: New cell Precoder-cyclingprecoding based specific and relay station may apply to R- transmissionusing M common RS (M antenna PDCCH (Q transmission antenna ports may bedefined in subcarrier level, ports (M = 2, 4, or 8) given OFDM symbolwhere Q is a area) positive integer) Case-5.2: Cell specific RS (CRS)conventionally defined in LTE release 8/9 (M antenna ports in backhaullink) Case-6 Rank 1 open loop layer #P pattern precoded Precoder cyclingprecoding based DM-RS for R-PDSCH may be used for R- transmission usingM demodulation (P = 0, 1, 2, PDCCH and transmission antenna 3, 4, 5, 6,7, or 8; e.g. reference signal (Q ports (M = 2, 4, or 8) P = 0 or 1)subcarrier level, where Q is a positive integer) precoded DM-RS layerpattern may use the same precoder as precoder for R- PDCCH transmissionCase-7 Transmission mode the Precoded DM-RS pattern same as R-PDSCH: forR-PDSCH closed loop spatial demodulation multiplexing Case-8Transmission mode the Precoded DM-RS pattern same as R-PDSCH: open forR-PDSCH loop spatial multiplexing demodulation Case-9 Closed loopprecoding Case-9.1: New cell based transmission using specific and relaystation M transmission antenna common RS (M antenna ports (M = 2, 4, or8) ports may be defined in given OFDM symbol area) Case-9.2: Cellspecific RS (CRS) conventionally defined in LTE release 8/9 (M antennaports in backhaul link) Case-10 Rank 2 closed loop Predetermined orgiven Precoded DM-RS precoding based two layer patterns C, D levelpattern may transmission for M of precoded DM-RS for use the sametransmission antenna R-PDSCH demodulation precoder as ports (M = 2, 4,or 8) (C≠D, C or D = 0, 1, 2, 3, precoder for R- 4, 5, 6, 7, or 8; e.g.C = 0 PDCCH and D = 1) transmission Case-11 Rank 2 open loop Case-11.1:New cell Precoder cycling precoding based specific and relay station maybe used for R- transmission for M common RS (M antenna PDCCH (Qtransmission antenna ports may be defined in subcarrier level, ports (M= 2, 4, or 8) given OFDM symbol where Q is a area) positive integer)Case-11.2: Cell specific RS (CRS) conventionally defined in LTE release8/9 (M antenna ports in backhaul link) Case-12 Rank 2 open loopPredetermined or given Precoder cycling precoding based two layerpatterns C, D may be used for R- transmission for M of precoded DM-RSfor PDCCH and transmission antenna R-PDSCH demodulation reference signal(Q ports (M = 2, 4, or 8) (C≠D, C or D = 0, 1, 2, 3, subcarrier level,4, 5, 6, 7, or 8; e.g. C = 0 where Q is a and D = 1) positive integer)precoded DM-RS layer pattern may use the same precoder as precoder forR- PDCCH transmission

In the above-described cases, a cell-specific and relay station-commonreference signal may be defined for demodulation and decoding of R-PDCCH(this will be described below with reference to FIGS. 24 to 26). As thecase may be, OFDM symbols defining the new reference signal may bedesignated. In the case that a precoded reference based transmissionmode applies to the R-PDSCH, a transmission mode designated byscheduling information for transmission in the frequency transmissionresource designated by scheduling and a precoded reference signalprecoded by its related precoding vector are used for demodulation anddecoding of R-PDSCH. On the contrary, for R-PDCCH, a new cell-specificand relay station-common reference signal may be used. Accordingly, theR-PDCCH and R-PDSCH may perform demodulation and decoding usingdifferent reference signals. That is, different forms or differentnumbers of reference signals may be used in the R-PDCCH area and R-PDSCHarea.

FIG. 18 illustrates an example of allocating cell-specific and relaystation-common reference signal patterns to an area in which the R-PDCCHis transmitted in the backhaul downlink subframe.

The backhaul subframe includes an access signal transmission section, aprotection section, and a backhaul receiving section. In the backhaulreceiving section, R-PDCCH and R-PDSCH are received. The R-PDCCH andR-PDSCH may be multiplexed in the backhaul receiving section of thebackhaul downlink subframe in any frequency resource area. In thiscircumstance, M M cell-specific and relay station-common referencesignals (hereinafter, “R-PDCCH reference signals”) patterns may beallocated in S OFDM symbol sections of the backhaul downlink subframe,where S is a natural number between 1 and 6. The S OFDM symbols areshown as consecutive OFDM symbols in FIG. 18, but the present inventionis not limited thereto. The S OFDM symbols may be spaced apart from eachother or a plurality of OFDM symbols may be grouped so that the groupsof symbols may be spaced apart from each other.

Further, the locations of the S OFDM symbols used for R-PDCCHtransmission in the backhaul downlink subframe may be fixed. In thiscase, an offset may be located on a per-OFDM symbol basis between theprotection section and a symbol from which R-PDCCH transmission begins.The OFDM symbol(s) over the offset may be used for transmission ofphysical signals such as reference signal, transmission of physicalcontrol channels or R-PDSCH transmission.

The R-PDCCH reference signal may be used for demodulation and decodingof the R-PDCCH. The physical resource mapping of the R-PDCCH referencesignal may be performed using one of methods to be described below.

First Embodiment

M (1) cell-specific and relay station-common reference signal detailedpatterns for R-PDCCH demodulation and decoding which are newly definedover the S OFDM symbols may be defined in the R-PDCCH transmissionresource area set semi-statically and mapped to the physical resources.The R-PDCCH transmission resource area may include basic units havingconsecutive frequency resources in the frequency domain. That is, theR-PDCCH transmission resource area may include plural basic units in thefrequency domain wherein the basic unit is the granularity. For suchbasic units, fixed reference patterns may be defined. For example, inthe case that the R-PDCCH transmission resource area is set so that thebasic unit is a PRB (Physical Resource Block), the reference signalpatterns for R-PDCCH demodulation and decoding may be fixed and definedon a per-PRB basis.

Second Embodiment

M (1) cell-specific and relay station-common reference signal detailedpatterns for R-PDCCH demodulation and decoding which are defined overthe S OFDM symbols may be defined in the entire system band or afrequency band set semi-statically (or statically) and mapped tophysical resources. The entire system band may be defined as a singlecomponent carrier band or a band which is a combination of pluralcomponent carriers.

The M R-PDCCH reference signal patterns may be patterns that are mappedwith the physical resources (for example, resource elements orsubcarriers) fixed on a per-PRB basis. The base station may map thePDSCH data modulation symbols to resource elements other than resourceelements mapped with the R-PDCCH reference signal patterns in the ratematching form in the band at which the PDSCH is transmitted among theentire system band. The LTE-A terminal may conduct demodulation anddecoding on resource elements mapped with the PDSCH data modulationsymbols. In the band at which the PDSCH is transmitted among the entiresystem band, the base station may puncture the resource elements mappedwith the R-PDCCH reference signal patterns and then transmit thepunctured resource elements. The legacy terminal (LTE terminal) mayperform decoding without recognizing whether the resource elementsmapped with the R-PDCCH reference signal patterns are punctured.

In the above example, the section of S OFDM symbols may be defined tohave the same number as the number of the OFDM symbols in which theR-PDCCH is transmitted or the R-PDCCH transmission symbol index.However, as the case may be, the section of S OFDM symbols may bedefined differently. For example, the number of the OFDM symbols inwhich the R-PDCCH is transmitted may be more than S. Such setting may bemade to be specific to the cell or relay station. The number of the OFDMsymbols in which the R-PDCCH is transmitted may be set to have a valueless than S.

The method described in connection with FIG. 18 (for example, thedescription on the R-PDCCH reference signal patterns) may also apply toconfiguring the R-PDCCH as described in connection with FIGS. 11 to 17.

Hereinafter, each case in Table 3 is described in greater detail.

1. Case-0

In Case-0, the base station uses single antenna transmission or transmitdiversity adopting M (M=1, 2, or 4) transmission antenna ports in theR-PDCCH transmission mode and uses a cell specific reference signal(CRS, common reference signal) that is defined in the conventional LTErelease 8/9 as the R-PDCCH reference signal.

FIG. 19 illustrates an example of a cell specific reference signal forfour antenna ports in the subframe to which the normal CP applies. FIG.20 illustrates an example of a cell specific reference signal for fourantenna ports in the subframe to which the extended CP applies. Theresource elements marked with RX in FIGS. 19 and 20 refer to referencesignal resource elements for antenna ports #X (X=0, 1, 2, or 3). FIGS.19 and 20 illustrate examples of the conventional cell specificreference signals. See section.6.10.1 in 3GPP TS 36.211 V8.4.0 (2008-09)Technical Specification Group Radio Access Network; Evolved UniversalTerrestrial Radio Access (E-UTRA); Physical Channels and Modulation(Release 8). Hereinafter, the conventional cell specific referencesignal may refer to the reference signal shown in FIGS. 19 and 20.

The relay station may use part of the conventional cell specificreference signal in the case of demodulating and decoding the R-PDCCH.The relay station may use the conventional cell specific referencesignal as the R-PDCCH reference signal. In the case that the basestation transmits the R-PDCCH using one, two, or four antenna ports, therelay station performs demodulating and decoding using the conventionalcell specific reference signal included in the S OFDM symbol area.Specifically, when the base station transmits the R-PDCCH using antennaport #0 and antenna port #1, the relay station may use the referencesignal resource elements arranged in the fifth OFDM symbol of the firstslot and the first and fifth OFDM symbols of the second slot in thebackhaul subframe. When the base station transmits the R-PDCCH usingantenna ports #2 and #3, the relay station may additionally use thereference signal resource elements arranged in the second OFDM symbol ofthe second slot in the backhaul subframe.

Table 4 below represents exemplary antenna ports applying according toM.

TABLE 4 Value of M Antenna port indices 1 Conventional cell specificreference signal antenna port #0 (Legacy CRS antenna port #0) 2Conventional cell specific reference signal antenna ports #0 and#1(Legacy CRS antenna port #0 and #1) 4 Conventional cell specificreference signal antenna ports #0, #1, #2, #3 (Legacy CRS antenna port#0, #1, #2, and #3)

In the backhaul downlink subframe, depending on the R-PDCCH transmissionarea (OFDM symbol area) set cell-specifically or relaystation-specifically, the OFDM symbol range of the conventional cellspecific reference signals (hereinafter, “CRS”) used fordemodulation/decoding of R-PDCCH may be determined. For example, 1) theR-PDCCH transmission area may include only the fifth OFDM symbol of thefirst slot, or 2) may include the fifth OFDM symbol of the first slot tothe first or second OFDM symbol of the second slot. In the case thatM=2, regarding 1) above, the relay station may conductdemodulation/decoding of the R-PDCCH using only CRS antenna ports #0 and#1 mapped with the fifth OFDM symbol of the first slot. Or regarding 2),the relay station may demodulate/decode the R-PDCCH using the CRSantenna ports #0 and #1 mapped with the fifth OFDM symbol of the firstslot and the first OFDM symbol of the second slot.

In the case that M=4, the relay station may demodulate/decode theR-PDCCH using the CRS antenna ports #0 and #1 mapped with the fifth OFDMsymbol of the first slot and the first OFDM symbol of the second slotand the CRS antenna ports #2 and #3 mapped with the second OFDM symbolof the second slot.

Transmit diversity schemes applicable by the base station include CDD(Cyclic Delay Diversity), PVS (precoding vector switching), STBC(SpaceTime Block Code), SFBC(Space Frequency Block Code), SFBC+FSTD (frequencyswitched transmit diversity), SFBC+CDD, STBC+FSTD, STBC+CDD, STBC+PVS,and so forth, and depending on M, may use other schemes. The CCD obtainsa diversity gain using each path delay between transmission antennas.The PVS is a sort of transmit diversity scheme and obtains a randombeam-forming gain by switching precoding vectors (weight) on aper-constant time, slot, or symbol basis. The SFBC efficiently appliesselectivity in the spatial domain and frequency domain to secure bothdiversity gain and multiple user scheduling gain in the correspondingdomain. The STBC applies selectivity in the spatial domain and timedomain. The FSTD distinguishes signals transmitted over multipleantennas for each frequency.

The number of R-PDCCH reference signal patterns for antenna ports usedfor the R-PDCCH may be defined to be the same as the number oftransmission antennas included in the base station. Or in considerationof the fact that the reference signal overhead of the backhaul downlinktransmission or the number of applicable reference signal patterns maybe set depending on the form of the backhaul downlink subframe, a lessnumber of R-PDCCH reference signal patterns than the number of thetransmission antennas included in the base station may be defined.

In the case that a less number of R-PDCCH reference signal patterns thanthe number of the transmission antennas in the base station are defined,the base station may use the antenna virtualization scheme for both dataand the reference signals. The “antenna virtualization” refers to ascheme that allows signals to appear to be transmitted through antennaswhose number is different from the number of actual transmissionantennas at the reception end. In other words, this scheme implementstransmission by setting the number of physical transmission antennasowned by the actual base station different from the number of virtualantennas (or the number of antenna ports) applied for the transmitter.At this time, a virtual antenna matrix for purposes of antennavirtualization is generally configured as (No. of physical transmissionantennas)×(No. of virtual antennas).

For example, the reference signal sequence #i (r_(i)(m)) may be formedto be mapped with virtual antenna #i. At this time, a virtual antennamatrix V may be used to map the reference signal sequence #i (r_(i)(m))with virtual antenna #i.

The number of the rows in the virtual antenna matrix may be the same asthe number of the physical transmission antennas, and the number ofcolumns in the virtual antenna matrix may be the same as the number ofthe virtual antennas. In the case that the reference signal for theterminal is transmitted in a virtual antenna mapping process, Nt (No. ofthe physical transmission antennas) virtual antennas may be configured.In this circumstance, the size of the virtual antenna matrix is Nt×Nt.

Equation 1 represents an example of the virtual antenna matrix where Ntis 8:

$\begin{matrix}{V = {\begin{pmatrix}v_{0} & v_{1} & \ldots & v_{7}\end{pmatrix} = \begin{pmatrix}v_{00} & v_{10} & \ldots & v_{70} \\v_{01} & v_{11} & \ldots & v_{71} \\\vdots & \vdots & \ddots & \vdots \\v_{07} & v_{17} & \ldots & v_{77}\end{pmatrix}}} & \left\lbrack {{Equation}\mspace{14mu} 1} \right\rbrack\end{matrix}$

Here, v_(i) refers to the virtual antenna vector #i for mapping thereference signal with the virtual antenna #i by the ith column vector inthe virtual antenna matrix. v_(ij) refers to a complex coefficient ofthe virtual antenna matrix (iε{0, 1, . . . , 7}, jε{0, 1, . . . , 7}).The complex coefficient may be configured in various forms depending onthe situation.

The virtual antenna matrix may be configured as a unitary matrix. In thecase that the virtual antenna matrix is a unitary matrix, electric powermay be distributed evenly to all of the transmission antennas.

The reference signal sequence vector #i in which the reference signalsequence #i is mapped with the virtual antenna #i may be represented asin Equation 2:

R _(i)(m)=v _(i) ·r _(i)(m),i=0, . . . ,7  [Equation 2]

Here, r_(i) (m) refers to the reference signal sequence #i, v_(i) thevirtual antenna vector #i as the i th column vector in the virtualantenna matrix, and R_(i)(m) the reference signal sequence vector #i.

The transmitter may transmit the reference signal sequence vector#i(R_(i)(m)) through Nt transmission antennas and the receiver mayreceive receiving signal vector y=[y₁ y₂ . . . y_(Nr)]^(T) through Nrreceiving antennas. The receiving signal vector y may be represented asin Equation 3:

$\begin{matrix}\begin{matrix}{y = {{H\; v_{i}{r_{i}(m)}} + n}} \\{= {{h_{i}{r_{i}(m)}} + n}}\end{matrix} & \left\lbrack {{Equation}\mspace{14mu} 3} \right\rbrack\end{matrix}$

Here, n=[n₁ n₂ . . . n_(Nr)]^(T) is a noise vector.

The receiver is formed to estimate the virtual antenna channel #i(h_(i))that is a virtual antenna channel for the virtual antenna #i from thereceiving signal vector. The receiver may estimate the virtual antennachannel #i(h_(i)) because of being aware of the reference signalsequence #i(r_(i)(m)).

Although illustrated herein is an example where one reference signalsequence is transmitted through one virtual antenna, K reference signalsequences may be transmitted through K virtual antennas. In the casethat transmission through K antennas applies to any receiver, thetransmitter may configure Nt virtual antennas and select K virtualantennas to transmit the reference signals.

Based on respective K reference signal sequences and respective Kvirtual antenna vectors, respective K reference signal sequence vectorsare generated that may be transmitted through Nt transmission antennas.Here, the respective K virtual antenna vectors may be different columnvectors that are selected from the virtual antenna matrix. For instance,when the virtual antenna matrix is an 8×8 matrix, the K virtual antennavectors are configured as K column vectors in the 8×8 matrix and thevirtual antenna matrix applying to the K virtual antennas may be an 8×Kmatrix.

The virtual antenna matrix may use the same virtual antenna matrixwithout respect to K. Or different antenna matrixes may be useddepending on K. For instance, the base station may, for the terminal,use the same virtual antenna matrix or different virtual antennamatrixes depending on 1, 2, or 4 antenna transmission.

Hereinafter, a specific example of the virtual antenna matrix isdescribed.

1. In Case that Eight Virtual Antennas are Configured and Four VirtualAntennas are Selected

In the case that four antenna transmission applies to the receiver, thetransmitter may transmit the reference signals by configuring eightvirtual antennas and selecting four virtual antennas. In this case, thefollowing virtual antenna matrix may be configured.

Equation 4 is an example of the virtual antenna matrix:

$\begin{matrix}\begin{matrix}{V = \begin{pmatrix}v_{0} & v_{1} & \ldots & v_{7}\end{pmatrix}} \\{= \begin{pmatrix}1 & 0 & 0 & 0 & 1 & 0 & 0 & 0 \\0 & 1 & 0 & 0 & 0 & 1 & 0 & 0 \\0 & 0 & 1 & 0 & 0 & 0 & 1 & 0 \\0 & 0 & 0 & 1 & 0 & 0 & 0 & 1 \\1 & 0 & 0 & 0 & {- 1} & 0 & 0 & 0 \\0 & 1 & 0 & 0 & 0 & {- 1} & 0 & 0 \\0 & 0 & 1 & 0 & 0 & 0 & {- 1} & 0 \\0 & 0 & 0 & 1 & 0 & 0 & 0 & {- 1}\end{pmatrix}}\end{matrix} & \left\lbrack {{Equation}\mspace{14mu} 4} \right\rbrack\end{matrix}$

In this case, the virtual antenna vector is fixed irrespective of thelocation of the time-frequency resources. Regardless of thetime-frequency resources, a specific beam is formed. Here, thetime-frequency resources may include subcarriers, resource elements, orspecific resources.

Equation 5 is another example of the virtual antenna matrix:

$\begin{matrix}{V = \begin{pmatrix}1 & 0 & 0 & 0 & 1 & 0 & 0 & 0 \\0 & 1 & 0 & 0 & 0 & 1 & 0 & 0 \\0 & 0 & 1 & 0 & 0 & 0 & 1 & 0 \\0 & 0 & 0 & 1 & 0 & 0 & 0 & 1 \\{\exp \left( {j\; d_{1}k} \right)} & 0 & 0 & 0 & {\sim {\exp \left( {j\; d_{1}k} \right)}} & 0 & 0 & 0 \\0 & {\exp \left( {j\; d_{2}k} \right)} & 0 & 0 & 0 & {\sim {\exp \left( {j\; d_{2}k} \right)}} & 0 & 0 \\0 & 0 & {\exp \left( {j\; d_{3}k} \right)} & 0 & 0 & 0 & {\sim {\exp \left( {j\; d_{3}k} \right)}} & 0 \\0 & 0 & 0 & {\exp \left( {j\; d_{4}k} \right)} & 0 & 0 & 0 & {\sim {\exp \left( {j\; d_{4}k} \right)}}\end{pmatrix}} & \left\lbrack {{Equation}\mspace{14mu} 5} \right\rbrack\end{matrix}$

Here, k refers to the time-frequency resource index indicating thetime-frequency resource, and di the phase (0≦d_(i)<2π, i=1, 2, 3, 4).For example, k may be a subcarrier index, resource element index, orspecific resource index. Depending on the time-frequency resources, thebeam may be formed.

A different type of matrix may be used as the virtual antenna matrix.For example, the virtual antenna matrix may be a combination of a phasediagonal matrix and a constant modulus matrix. The constant modulusmatrix is a matrix in which each element in the matrix has samemagnitude that is not ‘0’. For example, the constant modulus matrix Umay be a DFT (Discrete Fourier Transform) matrix or Walsh matrix. Forinstance, the virtual antenna matrix may be represented as in Equation6:

$\begin{matrix}{V = {\begin{pmatrix}{\exp \left( {j\; d_{0}k} \right)} & 0 & 0 & 0 & 0 & 0 & 0 & 0 \\0 & {\exp \left( {j\; d_{1}k} \right)} & 0 & 0 & 0 & 0 & 0 & 0 \\0 & 0 & {\exp \left( {j\; d_{2}k} \right)} & 0 & 0 & 0 & 0 & 0 \\0 & 0 & 0 & {\exp \left( {j\; d_{3}k} \right)} & 0 & 0 & 0 & 0 \\0 & 0 & 0 & 0 & {\exp \left( {j\; d_{4}k} \right)} & 0 & 0 & 0 \\0 & 0 & 0 & 0 & 0 & {\exp \left( {j\; d_{5}k} \right)} & 0 & 0 \\0 & 0 & 0 & 0 & 0 & 0 & {\exp \left( {j\; d_{6}k} \right)} & 0 \\0 & 0 & 0 & 0 & 0 & 0 & 0 & {\exp \left( {j\; d_{7}k} \right)}\end{pmatrix}U}} & \left\lbrack {{Equation}\mspace{14mu} 6} \right\rbrack\end{matrix}$

Here, matrix U is a constant modulus matrix, k the time-frequencyresource index indicating the time-frequency resource, and d_(i) thephase (0≦d_(i)<2π, i=0, 1, . . . , 7). The constant modulus matrix maybe a unitary matrix in which each element in the matrix has the samemagnitude. k may be a subcarrier index, resource element index, orspecific resource index.

In the case that phase d_(i) is ‘0’ (i=0, 1, . . . , 7), the virtualantenna matrix V becomes U. Phase d_(i) may use a fixed value or may bedetermined by the base station (i=0, 1, . . . , 7).

In case that eight virtual antennas are configured and two virtualantennas are selected.

In the case that two antenna transmission applies to the receiver, thetransmitter may configure eight virtual antennas and select two virtualantennas to transmit the reference signals. In this case, the followingvirtual antenna matrix may be configured.

Equation 7 is an example of the virtual antenna matrix:

$\begin{matrix}\begin{matrix}{V = \begin{pmatrix}v_{0} & v_{1} & \ldots & v_{7}\end{pmatrix}} \\{= \begin{pmatrix}1 & 0 & 1 & 0 & 1 & 0 & 1 & 0 \\0 & 1 & 0 & 1 & 0 & 1 & 0 & 1 \\1 & 0 & j & 0 & {- 1} & 0 & {- j} & 0 \\0 & 1 & 0 & j & 0 & {- 1} & 0 & {- j} \\1 & 0 & {- 1} & 0 & 1 & 0 & {- 1} & 0 \\0 & 1 & 0 & {- 1} & 0 & 1 & 0 & {- 1} \\1 & 0 & {- j} & 0 & {- 1} & 0 & j & 0 \\0 & 1 & 0 & {- j} & 0 & {- 1} & 0 & j\end{pmatrix}}\end{matrix} & \left\lbrack {{Equation}\mspace{14mu} 7} \right\rbrack\end{matrix}$

The virtual antenna matrix may be configured by expanding the DFT matrixor Walsh matrix. For instance, the virtual antenna matrix may berepresented as in Equation 8:

$\begin{matrix}\begin{matrix}{V = \begin{pmatrix}v_{0} & v_{1} & \ldots & v_{7}\end{pmatrix}} \\{= {\begin{pmatrix}D_{4 \times 4} & 0 \\0 & D_{4 \times 4}\end{pmatrix}\mspace{14mu} {or}\mspace{14mu} \begin{pmatrix}W_{4 \times 4} & 0 \\0 & W_{4 \times 4}\end{pmatrix}}}\end{matrix} & \left\lbrack {{Equation}\mspace{14mu} 8} \right\rbrack\end{matrix}$

Here, D_(4×4) is a 4×4 DFT matrix, and W_(4×4) is a 4×4 Walsh matrix. Assuch, the virtual antenna matrix may be configured by expanding the DFTmatrix or Walsh matrix in the block diagonal form. As such, the virtualantenna matrix may be configured differently depending on the number oftransmission antennas supported by the transmitter. Or one or morevirtual antenna matrixes for a specific number (e.g., 1, 2, or 4) oftransmission antennas may be configured. In such circumstances,different virtual antenna matrix may be used depending on thetransmission scheme, subframe, radio frame, or the like.

Or the base station may transmit the R-PDCCH by setting the number ofvirtual antennas or physical antennas used for transmission equal to thenumber (M) of the R-PDCCH reference signals. M may be set by the cellspecific and relay station common RRC signaling or by the systeminformation, or may be set by L1/L2 control information signaling. M maybe set differently for each relay station or each group of relaystations. At this time, M may be set by the relay station specific RRCsignaling or L1/L2 control information signaling.

2. Case-1

In Case-1, the base station uses single antenna transmission or transmitdiversity adopting M (M=1, 2, 4, or 8) transmission antenna ports as theR-PDCCH transmission mode and uses as the R-PDCCH reference signal a newcell specific and relay station common reference signal.

The new cell specific and relay station common reference signal may bemapped in the S OFDM symbol area and then transmitted in FIG. 18. Asdescribed above, the new cell specific and relay station commonreference signal will be described below (refer to FIGS. 24 to 26).Transmit diversity schemes applicable to the base station may includeCDD, PVS, STBC, SFBC, SFBC+FSTD, SFBC+CDD, STBC+FSTD, STBC+CDD, andSTBC+PVS, and may use other methods depending on M.

The number of the R-PDCCH reference signal patterns may be defined to beequal to the number of the transmission antennas in the base station. Orin consideration of the fact that the reference signal overhead of thebackhaul downlink transmission and the number of applicable referencesignal patterns may be set depending on the form of the backhauldownlink subframe, a less number of R-PDCCH reference signal patternsthan the number of transmission antennas in the base station may bedefined.

When a less number of R-PDCCH reference signal patterns than the numberof the transmission antennas in the base station is defined, the basestation may use antenna virtualization. At this time, the antennavirtualization may apply to both the R-PDCCH and R-PDSCH. Or the basestation may transmit the R-PDCCH with the number of virtual antennas orphysical antennas used for transmission set to be equal to the number(M) of the R-PDCCH reference signal patterns. M may be set by the cellspecific and relay station common RRC signaling or by the systeminformation, or may be set by L1/L2 control information signaling. M maybe set differently for each relay station or each group of relaystations. At this time, M may be set by the relay station specific RRCsignaling or L1/L2 control information signaling.

3. Case-2

In Case-2, the base station uses precoded transmit diversity adopting inthe R-PDCCH transmission mode R (R=1, 2, or 4) virtual antennal portsand uses as the R-PDCCH reference signal the precoded (or virtualized)relay station specific DM-RS.

The base station performs antenna virtualization by applying relaystation specific precoding to the transmission antennas. Through theantenna virtualization, the base station sets R virtual antennas andtransmits the R-PDCCH in the transmit diversity scheme. At this time,transmit diversity schemes applicable to the base station include, inthe case that R=2, CDD, PVS, STBC, and SFBC, and in the case that R=4,SFBC+FSTD, SFBC+CDD, STBC+FSTD, STBC+CDD, STBC+PVS, SFBC, STBC, PVS, andCDD. At this time, the number of DM-RS patterns applying fordemodulation/decoding of the R-PDCCH may be R. The R DM-RS patterns mayinclude patterns that have been applied with a precoder for antennavirtualization, and frequency-specifically apply over the R-PDCCHtransmission resources. R may be defined depending on the referencesignal overhead over the backhaul downlink subframe or the form of thebackhaul downlink subframe. The base station may set R in the upperlevel and inform it to the relay station through relay station specificor cell specific RRC signaling or signaling using relay station specificor cell specific L1/L2 control information.

In the case that the R-PDCCH and R-PDSCH for the same relay station aretransmitted in a FDM scheme, that is, when the R-PDCCH and R-PDSCH aretransmitted in different PRBs, as many precoded DM-RSs as the number ofR virtual antennas may apply to the PRB in which the R-PDCCH istransmitted, and then transmitted.

Or in the case that the R-PDCCH and R-PDSCH are multiplexed in theFDM/TDM scheme (refer to Alt 3 of FIG. 11), the R-PDCCH and R-PDSCH maybe multiplexed over any PRB. In this case, if the R-PDSCH is transmittedin the transmit diversity scheme, the R-PDSCH may be also transmittedlike the R-PDCCH in the same transmit diversity scheme using theprecoded DM-RS defined based on R virtual antennas. To transmit theR-PDSCH in the transmit diversity scheme, precoding vector informationfor designating and/or applying the transmission mode may be determinedby the base station. For this purpose, the base station may perform RRCsignaling or L1/L2 PDCCH control information signaling to a specificrelay station.

Or in the case that the R-PDCCH and R-PDSCH may be multiplexed in theTDM scheme over the backhaul downlink transmission frequency resource(refer to Alt 1 of FIG. 11), if the R-PDSCH is transmitted in theprecoding based spatial multiplexing transmission mode, one of thefollowing two embodiments may apply.

First embodiment: when the first embodiment applies, the rank value ofthe R-PDSCH for the precoding based spatial multiplexing transmission isequal to or more than R. Such situation may selectively occur in thebackhaul downlink subframe through setting of the R-PDCCH and R-PDSCH ormay also occur when the base station intentionally makes the R-PDSCHtransmission rank value equal to or more than R. Under suchcircumstances, the base station may transmit the R-PDCCH by one of thefollowing two methods:

Method 1: Any R DM-RS's used for demodulation and decoding of theR-PDCCH may be selected from precoded DM-RS's whose number is set as thenumber of rank values defined in the R-PDSCH transmission. At this time,various methods may apply to select the R precoded DM-RS's. For example,the R precoded DM-RS's may be selected in ascending order from theminimum RS index of the precoded DM-RS's. At this time, precodingapplied to the R-PDCCH for antenna virtualization may be defined by theprecoding vectors applied to the selected R DM-RS's and applied.

Method 2: Any R DM-RS's used for demodulation and decoding of theR-PDCCH may be selected from precoded DM-RS's whose number is set as thenumber of rank values defined in the R-PDSCH transmission (At this time,like in Method 1, various methods may apply to select the R precodedDM-RS's. For example, the R precoded DM-RS's may be selected inascending order from the minimum RS index of the precoded DM-RS's). Inthe reference signal patterns for the selected R DM-RS's, referencesignal resource elements (RS RE's) applicable to demodulation/decodingof the R-PDCCH are grouped. Such grouping may be conducted over the OFDMtransmission symbols. The reference signal resource elements (RS RE's)over the reference signal resource element groups may be subjected toprecoding for other antennal virtualization and other DM-RS's.

Second embodiment: the second embodiment applies when a rank value ofthe R-PDSCH for precoding based spatial multiplexing transmission isless than R. In this case, the base station may transmit the R-PDCCH byone of the following two methods:

Method 1: R DM-RS's used for demodulation and decoding of the R-PDCCHinclude all of the precoded DM-RS's whose number is set as the number(referred to as “P”) of rank values defined in the R-PDSCH transmission,and (R-P) necessary DM-RS's may be further defined and transmitted.Based on the precoding applied for the DM-RS's, precoding for antennavirtualization over the R-PDCCH may apply.

Method 2: R DM-RS's used for demodulation and decoding of the R-PDCCHincludes all of the precoded DM-RS's whose number is set as the number(referred to as “P”) of rank values defined in the R-PDSCH transmission,and (R-P) necessary DM-RS's may be further defined and transmitted. Inthe reference signal patterns for the R DM-RS's selected through theabove procedure, reference signal resource elements (RS SE's) applicableto demodulation/decoding of the R-PDCCH are grouped. Such grouping maybe conducted over the OFDM transmission symbols. The reference signalresource elements (RS RE's) over the reference signal resource elementgroups may be subjected to precoding for antenna virtualization of otherDM-RS's and other antennal virtualization and transmitted.

Third embodiment: in the case that the R-PDCCH is transmitted in thetransmit diversity scheme based on R virtual antennas, a transmissionrank and transmission method of the R-PDSCH may be defined. The basestation may designate the transmission rank value through UL grant orsemi-static signaling and notify the designated rank value to the relaystation. When the R-PDSCH transmission rank value is designated to bemore than R (for example, when P is designated as the rank value), thebase station conducts precoding based spatial multiplexing transmissionbased on the corresponding rank value (e.g., P) upon R-PDSCHtransmission. At this time, a receiving entity, for example, the relaystation receives the signal according to precoding based spatialmultiplexing based on the rank value (P).

In the case that in Third embodiment, the transmission rank value of theR-PDSCH is designated (through downlink channel allocation controlinformation signaling such as RRC signaling or L1/L2 PDCCH controlinformation signaling) to have a value (e.g., Q) less than R, the sametransmit diversity scheme as that applied for the R-PDCCH may apply tothe R-PDSCH transmission based on the R virtual antennas. This case maybe referred to as a “fall-back mode”. The fall-back mode may bedynamically or semi-statically designated upon application of thetransmission method and may be then applied. The base station may notifythe relay station through signaling that such transmission is carriedout. Or when the R-PDSCH transmission mode is designated as theprecoding based spatial multiplexing transmission mode, the R-PDCCHtransmission mode is designated as the transmit diversity based on the Rvirtual antennas, and the transmission rank value of the R-PDSCH is lessthan R, explicit signaling may be performed in order for the R-PDSCHtransmission mode to be designated as the same transmission mode as thatapplied for the R-PDCCH. That is, to operate in the fall-back mode maybe explicitly signaled. The signaling method may include RRC signaling,L1/L2 downlink channel allocation PDCCH signaling or explicitlynotifying the fall-back mode through an MAC message, or implicitlynotifying the fall-back mode through construction of other controlinformation.

4. Case-3.1

Case-3.1 happens when the base station uses rank-1 closed loop precodingbased transmission with M (M=2, 4, or 8) transmission antenna ports asthe R-PDCCH transmission mode and uses a new cell specific and relaystation common reference signal as the R-PDCCH reference signal.

Unlike the above-mentioned cases, the rank-1 precoding transmission modein Case 3-1 may apply to R-PDCCH transmission. At this time, theapplying precoder (that is, precoding matrix/vector) may be based on thefeedback information measured by the relay station or may be appliedwith wideband PMI or subband PMI according to indication or overridingof the base station independently from or together with the feedbackinformation. At this time, the cycle (or frequency) of the basestation's signaling and the feedback of the relay station may be set tobe long (that is, to have a lower frequency) or to be short (that is, tohave a higher frequency) compared to the feedback of the terminal andsignaling cycle of the base station, and especially, the base station'ssignaling may be conducted through RRC signaling or system informationin a cell specific and relay station common manner and may be conductedthrough RRC signaling in a relay station specific manner. Alternatively,L1/L2 signaling may be conducted, that is, the signaling may beperformed through PDCCH or MAC messaging. The new cell specific andrelay station common reference signal may apply to demodulation/decodingof the R-PDCCH. The reference signal may not be applied with precoding,but under a certain circumstance, the reference signal may be precodedby a precoding vector designated over the reference signal physicalresource.

The number of reference signal patterns for antenna ports used for theR-PDDCH may be M. M may be equal to the number of transmission antennasin the base station, but considering the form of the backhaul downlinksubframe or reference signal overhead, may be set to be less than thenumber of the transmission antennas in the base station.

In the case that a less number of reference signal patterns than thenumber of the transmission antennas of the base station are defined, thebase station may use antenna virtualization for both data and referencesignals. Or the base station may set the number of physical antennas orvirtual antennas used for transmission equal to the number (M) of thereference signal patterns to transmit the R-PDCCH. M may be set throughthe cell specific and relay station common RRC signaling, systeminformation, or L1/L2 control information signaling. M may be differentfor each relay station or each group of relay stations. At this time, Mmay be set through the relay station specific RRC signaling or L1/L2control information signaling.

5. Case-3.2

Case-3.2 occurs when the base station uses as the R-PDCCH transmissionmode the rank-1 closed loop precoding based transmission with M (M=2, 4,or 8) transmission antenna ports and uses the conventional cell specificreference signal as the R-PDCCH reference signal.

The rank-1 precoding transmission mode may apply to R-PDCCHtransmission. At this time, the applying precoder (that is, precodingmatrix/vector) may be based on the feedback information measured by therelay station or may be applied with wideband PMI or subband PMIaccording to indication or overriding of the base station independentlyfrom or together with the feedback information. At this time, the cycle(or frequency) of the base station's signaling and the feedback of therelay station may be set to be long or short compared to the feedback ofthe terminal and signaling cycle of the base station, and especially,the base station's signaling may be conducted through RRC signaling orsystem information in a cell specific and relay station common mannerand may be conducted through RRC signaling in a relay station specificmanner. Alternatively, L1/L2 signaling may be conducted, that is, thesignaling may be performed through PDCCH or MAC messaging. Theconventional cell specific reference signal may be used fordemodulation/decoding of the R-PDCCH, and the embodiment in Case-0 maylikewise apply. No precoding may apply to the cell specific referencesignal for demodulation/decoding of the R-PDCCH, but under a certaincircumstance, the cell specific reference signal may be precoded by aprecoding vector designated over the reference signal physical resource.

The number of reference signal patterns for antenna ports used for theR-PDDCH may be M. The number of the reference signal patterns may beequal to the number of transmission antennas in the base station, butconsidering the form of the backhaul downlink subframe or referencesignal overhead, may be set to be less than the number of thetransmission antennas in the base station.

In the case that a less number of reference signal patterns than thenumber of the transmission antennas of the base station are defined, thebase station may use antenna virtualization for both data and referencesignals. Or the base station may set the number of physical antennas orvirtual antennas used for transmission equal to the number (M) of thereference signal patterns to transmit the R-PDCCH. M may be set throughthe cell specific and relay station common RRC signaling, systeminformation, or L1/L2 control information signaling. M may be differentfor each relay station or each group of relay stations. At this time, Mmay be set through the relay station specific RRC signaling or L1/L2control information signaling.

6. Case-4

Case-4 occurs when the base station uses as the R-PDCCH transmissionmode the rank-1 closed loop precoding based transmission with M (M=2, 4,or 8) transmission antenna ports and uses as the R-PDCCH referencesignal the precoded DM-RS #P (P=an integer between 0 and 8, for example,P=0 or 1) level patterns for demodulation of the R-PDSCH.

The rank-1 precoding transmission mode may apply to R-PDCCHtransmission. At this time, the applying precoder (that is, precodingmatrix/vector) may be based on the feedback information measured by therelay station or may be applied with wideband PMI or subband PMIaccording to indication or overriding of the base station independentlyfrom or together with the feedback information. At this time, the cycle(or frequency) of the base station's signaling and the feedback of therelay station may be set to be long or short compared to the feedback ofthe terminal and signaling cycle of the base station, and especially,the base station's signaling may be conducted through RRC signaling orsystem information in a cell specific and relay station common mannerand may be conducted through RRC signaling in a relay station specificmanner. Alternatively, L1/L2 signaling may be conducted, that is, thesignaling may be performed through PDCCH or MAC messaging.

At this time, the reference signal for demodulation/decoding of theR-PDCCH may be applied with the pattern for a single layer (or a singletransmission stream) of the precoded DM-RS for the R-PDSCH. The DM-RSpattern for the single layer may be determined based on the number oftransmission antennas included in the base station. Assuming that theDM-RS pattern for the single layer is a DM-RS pattern for the level #P,P may be an integer between 0 and 8—for example, P=0 or 1.

What layer the DM-RS pattern is used for may be designated in a cellspecific and relay station common manner or in a relay station specificmanner. In the cell specific and relay station common manner, suchdesignation may be conducted through the cell specific and relay stationcommon RRC signaling or system information or L1/L2 control informationsignaling. If the designation is performed in the relay station specificmanner, relay station specific RRC signaling or relay station specificL1/L2 control information signaling may apply. The precoding vector forthe single layer DM-RS pattern for R-PDCCH demodulation/decoding may beequal to the rank-1 wideband precoding vector or subband precodingvector applied for R-PDSCH transmission.

In the case that the R-PDCCH transmission mode is the rank-1 closed loopprecoding based transmission, the following embodiments may applydepending on the R-PDSCH transmission mode.

First embodiment: in the case that the R-PDSCH transmission applyingspecifically for the relay station or commonly for the relay stations inthe cell is transmit diversity or other non-precoding basedtransmission, the single layer DM-RS pattern applying to rank-1precoding transmission of the R-PDCCH may be applied with DM-RS patterns(P=0 or 1 or 2 or 3 or 4 or 5 or 6 or 7 or 8; for example, P=0 or 1) ofone layer #P applicable based the number of the transmission antennas inthe base station. This may be designated through separate signaling in acell specific and relay station common or relay station specific manner.For example, such designation may be conducted through RRC signaling,L1/L2 PDCCH control information signaling, or signaling through an MACmessage. At this time, the precoder (that is, precoding vector) appliedto the DM-RS used for R-PDCCH transmission may be designated in a cellspecific and relay station common or relay station specific mannerthrough separate signaling (for example, RRC signaling, L1/L2 PDCCHcontrol information signaling, or MAC message signaling) or may beapplied by a predetermined method as well.

Second embodiment: in the case that the R-PDSCH transmission applyingspecifically for the relay station or commonly for the relay stations inthe cell is precoding based spatial multiplexing (where, the spatialmultiplexing includes single user MIMO and multiuser MIMO), the singlelayer DM-RS pattern applying for the rank-1 precoding transmission ofthe R-PDCCH may be the DM-RS pattern of the single layer #P applicablebased on the number of the transmission antennas in the base station.Here, P may be an integer between 0 and 8—for example, P may be 0 or 1.The precoding for the R-PDCCH and the DM-RS pattern of the layer #P maybe constituted of the entire or specific one or more column vectors ofthe precoder (that is, precoding matrix) applying for R-PDSCHtransmission. At this time, the column vectors may be selected usinglayer index values of the layer DM-RS patterns of the DM-RS used forR-PDCCH transmission, or may be explicitly signaled or implicitly set asany value. In the case of explicit signaling, the designation may beperformed through separate signaling in a cell specific and relaystation common manner or relay station specific manner. For example,such designation may be performed through RRC signaling, L1/L2 PDCCHcontrol information signaling, or signaling with an MAC message.

7. Case-5.1

Case-5.1 happens when the base station uses rank-1 open loop precodingbased transmission with M (M=2, 4, or 8) transmission antenna ports asthe R-PDCCH transmission mode and uses a new cell specific and relaystation common reference signal as the R-PDCCH reference signal. At thistime, the applying precoding vector may be based on the long-term of therelay station and/or long-term indication or overriding of the basestation. At this time, such designation may be performed throughseparate signaling, such as RRC signaling, L1/L2 PDCCH controlinformation signaling, or signaling with an MAC message, in a cellspecific and relay station common or relay station specific manner.

The rank-1 precoding transmission mode may apply to the R-PDCCHtransmission. At this time, the applying precoder (that is, precodingmatrix/vector) may be determined based on the feedback information ofthe relay station or indication of the base station. Or the precoder maybe applied with precoding (vector) cycling. The precoding vector cyclingmeans that the whole or some of the rank-1 precoding vectors may besequentially applied with one or more subcarriers, groups of subcarriers(which may be represented in plural PRB units) or the minimum unit ofphysical resources designated consecutively for R-PDCCH transmission.For M transmission antenna ports, the reference patterns of the new cellspecific and relay station common reference signal defined in the S OFDMsymbols are used for demodulation/decoding of the R-PDCCH. The referencesignal may not be subjected to precoding or under a certain situation,may be precoded by the precoding vector designated over the referencesignal physical resource. At this time, the designated precoding vectoror a precoding vector set used upon application of the precoding vectorcycling may be predefined and then designated, but may be alternativelydesignated through separate signaling in a cell specific and relaystation common or relay station specific manner. For example, suchdesignation may be conducted through RRC signaling, L1/L2 PDCCH controlinformation signaling, or signaling with an MAC message.

The number of reference signal patterns for antenna ports used for theR-PDDCH may be M. The number of the reference signal patterns may beequal to the number of transmission antennas in the base station, butconsidering the form of the backhaul downlink subframe or referencesignal overhead, may be set to be less than the number of thetransmission antennas in the base station.

In the case that a less number of reference signal patterns than thenumber of the transmission antennas of the base station are defined, thebase station may use antenna virtualization for both data and referencesignals. Or the base station may set the number of physical antennas orvirtual antennas used for transmission equal to the number (M) of thereference signal patterns to transmit the R-PDCCH. M may be set throughthe cell specific and relay station common RRC signaling, systeminformation, or L1/L2 control information signaling. M may be differentfor each relay station or each group of relay stations. At this time, Mmay be set through the relay station specific RRC signaling or L1/L2control information signaling.

8. Case-5.2

Case-5.2 happens when the base station uses rank-1 open loop precodingbased transmission with M (M=2, 4, or 8) transmission antenna ports asthe R-PDCCH transmission mode and uses the conventional cell specificreference signal as the R-PDCCH reference signal. At this time, theapplying precoding vector may be based on the long-term of the relaystation and/or long-term indication or overriding of the base station.At this time, such designation may be performed through separatesignaling, such as RRC signaling, L1/L2 PDCCH control informationsignaling, or signaling with an MAC message, in a cell specific andrelay station common or relay station specific manner.

The rank-1 precoding transmission mode may apply to the R-PDCCHtransmission. At this time, the applying precoder (that is, precodingmatrix/vector) may be determined based on the feedback information ofthe relay station or indication of the base station. Or the precoder maybe applied with precoding (vector) cycling. At this time, the designatedprecoding vector or a precoding vector set used upon application of theprecoding vector cycling may be predefined and then designated, but maybe alternatively designated through separate signaling in a cellspecific and relay station common or relay station specific manner. Forexample, such designation may be conducted through RRC signaling, L1/L2PDCCH control information signaling, or signaling with an MAC message.

In such circumstances, M conventional cell specific reference signalpatterns may be used for demodulation/decoding of the R-PDCCH withrespect to M transmission antenna ports (similar to the above-describedCase-0). The reference signal may not be subjected to precoding, butunder a certain circumstance, may be precoded by the precoding vectordesignated over the reference signal physical resource.

The number of reference signal patterns for antenna ports used for theR-PDDCH may be M. The number of the reference signal patterns may beequal to the number of transmission antennas in the base station, butconsidering the form of the backhaul downlink subframe or referencesignal overhead, may be set to be less than the number of thetransmission antennas in the base station.

In the case that a less number of reference signal patterns than thenumber of the transmission antennas of the base station are defined, thebase station may use antenna virtualization for both data and referencesignals. Or the base station may set the number of physical antennas orvirtual antennas used for transmission equal to the number (M) of thereference signal patterns to transmit the R-PDCCH. M may be set throughthe cell specific and relay station common RRC signaling, systeminformation, or L1/L2 control information signaling. M may be differentfor each relay station or each group of relay stations. At this time, Mmay be set through the relay station specific RRC signaling or L1/L2control information signaling.

9. Case-6

Case-6 happens when the base station uses rank-1 open loop precodingbased transmission with M (M=2, 4, or 8) transmission antenna ports asthe R-PDCCH transmission mode and uses as the R-PDCCH reference signalthe layer pattern of precoded DM-RS #P (P is an integer between 0 and 8,e.g., P=0 or 1) for R-PDSCH demodulation. At this time, the applyingprecoding vector may be based on the long-term of the relay stationand/or long-term indication or overriding of the base station. At thistime, such designation may be performed through separate signaling, suchas RRC signaling, L1/L2 PDCCH control information signaling, orsignaling with an MAC message, in a cell specific and relay stationcommon or relay station specific manner.

The rank-1 precoding transmission mode may apply to the R-PDCCHtransmission. At this time, the applying precoder (that is, precodingmatrix/vector) may be determined based on the feedback information ofthe relay station or indication of the base station. Or the precoder maybe applied with precoding (vector) cycling. At this time, the designatedprecoding vector or a precoding vector set used upon application of theprecoding vector cycling may be predefined and then designated, but maybe alternatively designated through separate signaling in a cellspecific and relay station common or relay station specific manner. Forexample, such designation may be conducted through RRC signaling, L1/L2PDCCH control information signaling, or signaling with an MAC message.

At this time, the reference signal for demodulation/decoding of theR-PDCCH may be applied with the pattern for a single layer of theprecoded DM-RS for the R-PDSCH. The DM-RS pattern for the single layermay be determined based on the number of transmission antennas includedin the base station. Assuming that the DM-RS pattern for the singlelayer is a DM-RS pattern for the level #P, P may be an integer between 0and 8—for example, P=0 or 1.

What layer the DM-RS pattern is used for may be designated in a cellspecific and relay station common manner or in a relay station specificmanner. In the cell specific and relay station common manner, suchdesignation may be conducted through the cell specific and relay stationcommon RRC signaling or system information or L1/L2 control informationsignaling. If the designation is performed in the relay station specificmanner, relay station specific RRC signaling or relay station specificL1/L2 control information signaling may apply. The precoding for thesingle layer DM-RS pattern for R-PDCCH demodulation/decoding may beapplied with the same precoder as the rank-1 wideband precoder orsubband precoder applying for R-PDSCH transmission with respect to thecorresponding physical resource RE. Or the precoding may be conducted bythe rank-1 wideband precoder or subband precoder separately signaledfrom the base station in such a manner as being not applied with theprecoding vector cycling. The rank-1 wideband precoder or subbandprecoder may be defined as any column vector in a precoding matrix givenin the rank more than 1. At this time, the precoding vector may bedesignated, as described above, by the base station in a cell specificand relay station common manner or relay station specific manner. In acell specific and relay station common manner, such designation may beperformed through cell specific and relay station common RRC signalingor system information, or through L1/L2 control information signaling.

Under the situations applied with the R-PDCCH transmission mode asdescribed above, detailed transmission methods of the R-PDCCH andR-PDSCH may change depending on the transmission mode applied to theR-PDSCH.

First Embodiment: in the case that the R-PDSCH transmission mode is atransmit diversity or other non-precoding based transmission mode withrespect to a specific relay station or the whole relay stations, therank-1 precoding transmission mode may apply to the R-PDCCHtransmission. The precoder applying for the rank-1 precodingtransmission mode may be determined depending on the feedbackinformation of the relay station or indication or overriding of the basestation. Or the precoder may be determined by applying the precodingvector cycling in which the whole or some of the applicable rank-1precoding vectors may be sequentially applied with one or moresubcarriers, groups of subcarriers (which may be represented in pluralPRB units) or the minimum unit of physical resources designatedconsecutively for R-PDCCH. The precoding vector set applied for theprecoding vector cycling may be designated in a cell specific and relaystation common manner or relay station specific manner. In the cellspecific and relay station common manner, such designation may beperformed through cell specific and relay station common RRC signalingor system information or L1/L2 control information signaling. At thistime, the single precoded layer DM-RS pattern may apply. The singlelayer DM-RS pattern may be a DM-RS pattern of the single layer #Papplicable based on the number of transmission antennas included in thebase station. Here, P may be an integer between 0 and 8—for example, Pmay be 0 or 1.

What layer the DM-RS pattern is used for may be designated in a cellspecific and relay station common manner or in a relay station specificmanner. In the cell specific and relay station common manner, suchdesignation may be conducted through the cell specific and relay stationcommon RRC signaling or system information or L1/L2 control informationsignaling. If the designation is performed in the relay station specificmanner, relay station specific RRC signaling or relay station specificL1/L2 control information signaling may apply. The precoding vector forthe single layer DM-RS pattern for R-PDCCH demodulation/decoding may beequal to the rank-1 wideband precoding vector or subband precodingvector applied for R-PDSCH transmission. Or the precoding may beconducted by the rank-1 wideband precoder or subband precoder separatelysignaled from the base station in such a manner as being not appliedwith the precoding vector cycling. The rank-1 wideband precoder orsubband precoder may be defined as any column vector in a precodingmatrix given in the rank more than 1.

The selection of the column vector may be set depending on the layerindex value of the layer DM-RS pattern of the DM-RS used for R-PDCCHtransmission, but any value may be explicitly signaled or implied set.

Second embodiment: in the case that the R-PDSCH transmission mode isprecoding based spatial multiplexing (including SU-MIMO and MU-MIMOboth), the rank-1 precoding transmission mode may apply to the R-PDCCHtransmission. At this time, the applying precoder (that is, precodingmatrix/vector) may be determined based on the feedback information ofthe relay station or indication of the base station. Or the precoder maybe applied with precoding (vector) cycling. At this time, a precodingvector set used for the precoding vector cycling may be designated bythe base station in a cell specific and relay station common manner orrelay station specific manner. In the relay station common manner, suchdesignation may be performed through cell specific and relay stationcommon RRC signaling or system information or L1/L2 control informationsignaling.

At this time, the reference signal for demodulation/decoding of theR-PDCCH may be applied with the pattern for the single layer of theprecoded DM-RS. The DM-RS pattern for the single layer may be determinedbased on the number of the transmission antennas included in the basestation. Assuming that the DM-RS pattern for the single layer is a DM-RSpattern for the level #P, P may be an integer between 0 and 8—forexample, P=0 or 1.

What layer the DM-RS pattern is used for may be designated in a cellspecific and relay station common manner or in a relay station specificmanner. In the cell specific and relay station common manner, suchdesignation may be conducted through the cell specific and relay stationcommon RRC signaling or system information or L1/L2 control informationsignaling. If the designation is performed in the relay station specificmanner, relay station specific RRC signaling or relay station specificL1/L2 control information signaling may apply. The precoding for thesingle layer DM-RS pattern for R-PDCCH demodulation/decoding may beapplied with the same precoder as the rank-1 wideband precoder orsubband precoder applying for R-PDSCH transmission with respect to thecorresponding physical resource RE. Or the precoding may be conducted bythe rank-1 wideband precoder or subband precoder separately signaledfrom the base station in such a manner as being not applied with theprecoding vector cycling. The rank-1 wideband precoder or subbandprecoder may be defined as any column vector in a precoding matrix givenin the rank more than 1.

At this time, the R-PDSCH transmission may be applied with the rank-1open loop or more-than-rank 1 precoding transmission. Then, the precoderused for R-PDCCH transmission may be the same as the precoder used forR-PDSCH transmission, and depending on the rank value for R-PDSCHtransmission, may become the column vector in the precoding matrix usedfor R-PDSCH transmission. The selection of the column vector may be setdepending on the index value of the layer DM-RS pattern of the DM-RSused for R-PDCCH transmission or any value may be explicitly signaled orimplicitly set.

10. Case-7

Case-7 happens when the base station uses as the R-PDCCH transmissionmode the same transmission mode (for example, closed loop spatialmultiplexing) as the R-PDSCH transmission mode and uses as the R-PDCCHreference signal the precoded DM-RS pattern for the R-PDSCHdemodulation.

In the case that the closed loop spatial multiplexing transmission modeapplies to the R-PDSCH transmission to the relay station, the sameclosed loop spatial multiplexing transmission mode may apply as well forthe R-PDCCH transmission. At this time, R-PDCCH requires relatively highreliability over R-PDSCH. Accordingly, the R-PDCCH transmission may beperformed at a low rank (the number of transmission layers ortransmission streams) compared to the R-PDSCH transmission. The rankapplying for R-PDCCH may be set at an upper layer by the base station ina cell specific and relay station common or relay station specificmanner. In the case that information on the rank setting is set cellspecifically or relay station commonly, the information may betransferred to the relay station through cell specific and relay stationcommon RRC signaling or system information or L1/L2 control informationsignaling. In the case of being designated in a relay station specificmanner, the information on the rank setting may be transferred to therelay station through relay station specific RRC signaling or relaystation specific L1/L2 control information signaling. Information ondesignation of the precoder used for the corresponding R-PDCCHtransmission may also be set by the base station at an upper layer in arelay station specific manner. In such circumstances, the information ondesignation of the precoder may be transferred to the correspondingrelay station through relay station specific RRC signaling or relaystation specific L1/L2 control information signaling.

As many precoded layer DM-RS patterns as the rank value set for R-PDCCHtransmission may be used as reference signals for demodulation/decodingof the R-PDCCH. It is assumed that the rank value set for R-PDCCHtransmission is R. Then, R precoded layer DM-RS patterns may be selectedat the layer DM-RS designated uniquely for each applicable layer basedon the number of the transmission antennas in the base station. That is,among the layer #P DM-RS patterns (P=0 or 1 or 2 or 3 or 4 or 5 or 6 or7 or 8; for example P=0 or 1), as many patterns as R may be designatedand used. The selection of the R precoded layer DM-RS patterns may beperformed in a cell specific and relay station common or relay stationspecific manner. That is, when information on the designation is setcell specifically or relay station commonly, the information may betransferred to the relay station through cell specific and relay stationcommon RRC signaling or system information or L1/L2 control informationsignaling. Or when the information on the designation is designatedrelay station specifically, the information may be transferred to therelay station through relay station specific RRC signaling or relaystation specific L1/L2 control information signaling. At this time,precoding for the corresponding layer DM-RS pattern may be performedequally by the precoder designated together with the rank applying forR-PDCCH transmission. The precoder, as described above, may beexplicitly signaled by the base station or then set. However, theprecoder may be implied set such as, when R-PDSCH performs precodingbased transmission, a precoder used for R-PDSCH transmission or one ormore column vectors for the precoder. The selection of the column vectormay be determined (for example, equally determined) based on the layerindex value for the DM-RS pattern of the DM-RS used for R-PDCCHtransmission, or any value may be explicitly signaled or set implicitly.

11. Case-8

Case-8 happens when the base station uses as the R-PDCCH transmissionmode the same transmission mode as the R-PDSCH transmission mode (forexample, open loop spatial multiplexing) and uses as the R-PDCCHreference signal the precoded DM-RS pattern for R-PDSCH demodulation.

In the case that the open loop spatial multiplexing transmission modeapplies to the R-PDSCH transmission to the relay station, the sameclosed loop spatial multiplexing transmission mode may apply as well forthe R-PDCCH transmission. At this time, R-PDCCH requires relatively highreliability over R-PDSCH. Accordingly, the R-PDCCH transmission may beperformed at a low rank (the number of transmission layers ortransmission streams) compared to the R-PDSCH transmission. The rankapplying for R-PDCCH may be set at an upper layer by the base station ina cell specific and relay station common or relay station specificmanner. In the case that information on the rank setting is set cellspecifically or relay station commonly, the information may betransferred to the relay station through cell specific and relay stationcommon RRC signaling or system information or L1/L2 control informationsignaling. The precoder used for transmission of the correspondingR-PDCCH may be determined depending on feedback information of the relaystation or indication of the base station. Or the precoder may beapplied with precoding (vector) cycling. At this time, the informationon the precoding vector or information on one or more precoding vectorsets applied for the precoding vector cycling may be transmitted to therelay station through cell specific and relay station common RRCsignaling or system information or L1/L2 control information signaling.In the case that the corresponding information is designated relaystation specifically, the information may be transferred to the relaystation through relay station specific RRC signaling or relay stationspecific L1/L2 control information signaling.

As many precoded layer DM-RS patterns as the rank value set for R-PDCCHtransmission may be used as reference signals for demodulation/decodingof the R-PDCCH. It is assumed that the rank value set for R-PDCCHtransmission is R. Then, R precoded layer DM-RS patterns may be selectedat the layer DM-RS designated uniquely for each applicable layer basedon the number of the transmission antennas in the base station. That is,among the layer #P DM-RS patterns (P=0 or 1 or 2 or 3 or 4 or 5 or 6 or7 or 8; for example P=0 or 1), as many patterns as R may be designatedand used. The selection of the R precoded layer DM-RS patterns may beperformed in a cell specific and relay station common or relay stationspecific manner. That is, when information on the designation is setcell specifically or relay station commonly, the information may betransferred to the relay station through cell specific and relay stationcommon RRC signaling or system information or L1/L2 control informationsignaling. Or when the information on the designation is designatedrelay station specifically, the information may be transferred to therelay station through relay station specific RRC signaling or relaystation specific L1/L2 control information signaling. At this time,precoding for the corresponding layer DM-RS pattern may be performedequally by the precoder designated together with the rank applying forR-PDCCH transmission. Precoding for the corresponding layer DM-RSpattern may be applied with the rank-1 wideband precoder applied forR-PDCCH transmission with respect to individual reference signalresource element over the corresponding DM-RS pattern and a precoder thesame as the subband precoder. Unlike this, in such a manner as not beingapplied with the precoding vector cycling, the precoding may beperformed by the rank-1 wideband precoder or subband precoder separatelysignaled from the base station.

The precoder, as described above, may be explicitly signaled by the basestation or then set. However, the precoder may be implied set such as,when R-PDSCH performs precoding based transmission, a precoder used forR-PDSCH transmission or one or more column vectors for the precoder. Theselection of the column vector may be determined (for example, equallydetermined) based on the layer index value for the DM-RS pattern of theDM-RS used for R-PDCCH transmission, or any value may be explicitlysignaled or set implicitly.

12. Case-9/10/11/12

Case-9 to 12 are respectively the same as Case-3 to 6 in light oftransmission methods of the R-PDCCH and setting methods of DM-RS's usedfor demodulation/decoding of the R-PDCCH. The only difference is that inCases 3 to 6, the number of precoders (that is, precoding vectors) setfor R-PDCCH, the number of DM-RS layer RS patterns applied for R-PDCCHtransmission and the number of precoders applied for each of them areset as “1” whereas in Cases 9 to 12, the numbers are set as “2”. At thistime, setting methods may be the same as those suggested in Cases 3 to 6under the assumption that two precoders or DM-RS layer RS patterns donot overlap each other.

Various cases regarding transmission mode designation for R-PDCCH andtypes and patterns of reference signals applied for the R-PDCCHtransmission have been described so far. In such a manner that dependingon the number of transmission antennas in the base station (or cell) ortransmission mode, any case may be predetermined, the types or patternsof reference signals applied for R-PDCCH transmission and transmissionmode of the R-PDCCH may be set. As the case may be, one or more may beselected from the plural possible cases, and information on the selectedcase may be signaled in the form of upper layer signaling in a cellspecific and relay station common or relay station specific manner. Inthe case that the information on the selected case is cell specific andrelay station common, cell specific and relay station common RRCsignaling or system information or L1/L2 control information signalingmay apply. In the case that the information on the selected case isdesignated relay station specifically, relay station specific RRCsignaling or relay station specific L1/L2 control information signalingmay be performed.

Or alternatively, as mentioned in connection with some cases, dependingon the transmission mode designation of the R-PDSCH, the R-PDCCHtransmission mode case may be designated in a one-to-one mapping manner.If the R-PDSCH has an MU-MIMO transmission mode, allocation oftransmission physical resources of the R-PDCCH may be conductedindependently from the physical resource allocation of the R-PDSCH andmay be set as the transmission mode case of the R-PDCCH that has beenset corresponding to the number of streams applied for the correspondingrelay station over the MU-MIMO.

The above-described R-PDCCH transmission mode and description on thetypes and patterns for R-PDCCH demodulation/decoding are based upon theassumption that the structure of the backhaul downlink subframe providesbackward comparability for LTE terminals as shown in FIG. 18. That is,the relay station has a structure of allocating the resource to the LTEterminal over a first predetermined number of OFDM symbols in thebackhaul downlink subframe and then receiving signals from the basestation over the subsequent OFDM symbols with the protection section.However, the present invention is not limited thereto and may also applyto backhaul downlink subframe structures that do not provide backwardcompatibility to the LTE terminal. For example, a subframe structure maybe used in a multicarrier system, wherein for some carriers, a subframestructure considering backward compatibility to the LTE terminal asshown in FIG. 18 is used, and for other carriers, a subframe structurenot providing backward compatibility to the LTE terminal may be used. Atthis time, the above other carriers may also be applied with the R-PDCCHtransmission mode and the methods associated with the types and patternsof the reference signals for R-PDCCH demodulation/decoding according tothe present invention.

Although the above description suggests, in detail, the transmissionmethod of the R-PDCCH and types and patterns of the DM-RS used, thisshould not be construed as limited thereto. For instance, according tothe present invention, methods of transmitting PDCCH over carriers thatare not associated with monitoring or resource allocation to theexisting LTE release-8 terminals (such carriers may be referred to as“non-backward compatible carriers) and DM-RS patterns used may apply aswell. At this time, downlink subframes used over the non-backwardcompatible carriers may have a structure as described in connection withFIG. 6. Although in FIG. 6 three PDCCH transmission symbols are set, thepresent invention is not limited thereto and one or two symbols may beset. Or the present invention may apply to the backhaul downlinksubframe over the non-backward compatible carrier in association withthe transmission method of the R-PDCCH and DM-RS patterns used for thetransmission method. At this time, the target backhaul downlink subframemay have any one of the structures described in connection with FIGS. 11to 18, and may have other structures as well. These other subframestructures are described below.

FIGS. 21 to 23 illustrate examples of backhaul downlink subframestructures that do not provide backward compatibility.

Referring to FIG. 21, the backhaul downlink subframe includes protectionsections at first and end portions, and receives the R-PDCCH in S OFDMsymbols subsequent to the first protection section. Referring to FIG.22, the R-PDCCH is received in first S OFDM symbols in the backhauldownlink subframe that includes a protection section at the end portion.FIG. 23 is different from FIG. 21 in that in FIG. 23 the backhauldownlink subframe does not include a protection section at the endportion. The subframe structures shown in FIGS. 21 to 23 may apply tonon-backward compatible carriers.

New cell specific and relay station common reference signals aredescribed that are used as R-PDCCH reference signals fordemodulation/decoding of the R-PDCCH in Cases 1, 3.1, 5.1, 9.1, and 11.

FIGS. 24 to 26 illustrate new cell specific and relay station commonreference signals (simply referred to as “new reference signals”) thatmay be used as the R-PDCCH reference signals.

Referring to FIG. 24, the R-PDCCH area may include fourth OFDM symbolsto sixth OFDM symbols in the backhaul downlink subframe. In this case,the new reference signal is arranged in one OFDM symbol that does notoverlap RE (marked with R0 to R3) to which the conventional cellspecific reference signal is allocated. FIG. 24 illustrates an examplewhere a new reference signal is allocated in the fourth OFDM symbol ofthe backhaul downlink subframe. In this case, a code whose length is 12may be CDMed to twelve RE's and allocated in the fourth OFDM symbol tosupport up to eight transmission antenna ports.

FIG. 25 illustrates an example of a new reference signal supporting upto four transmission antenna ports. Four RE's are allocated for eachtransmission antenna port and the same RE is allocated for a pair oftransmission antenna ports (for example, transmission antenna ports #{0,1}, #{2,3}). However, different codes are CDMed and reference signalsfor pairs of transmission antenna ports may be distinguished from eachother. The new reference signal is arranged in two OFDM symbols that donot overlap the RE (marked with R0 to R3) to which the conventional cellspecific reference signal is allocated. For instance, the new referencesignal may be allocated in the fourth OFDM symbol and the sixth OFDMsymbol of the backhaul downlink subframe.

FIG. 26 illustrates an example of a new reference signal supporting upto eight transmission antenna ports. Four RE's are allocated for eachtransmission antenna port and the same RE may be allocated for a pair oftransmission antenna ports (for example, transmission antenna ports #{0,1}, #{2,3}, #{4,5}, #{6,7}). However, different codes may be CDMed andreference signals for the pairs of transmission antenna ports may bedistinguished from each other. The new reference signal is arranged intwo OFDM symbols that do not overlap the RE (marked with R0 to R3) towhich the conventional cell specific reference signal is allocated. Forinstance, the new reference signal may be allocated in the fourth OFDMsymbol and the sixth OFDM symbol of the backhaul downlink subframe.

Hereinafter, the downlink DM-RS is described.

The terminal specific DM-RS is a reference signal uniquely defined overthe downlink frequency resource that the base station allocates to anyterminal in any downlink subframe. The reference signal pattern of theDM-RS is defined on a PRB (Physical Resource Block) basis that is theminimum unit for the downlink frequency resource allocation. Thedownlink DM-RS defined so far is assumed to be used only in theprecoding based transmission mode among downlink MIMO transmission modesand assumed to be applied with the same precoding as precoding appliedover the data transmission RE (Resource Elements, that is, subcarriers).However, for any specific purposes, it may also be considered that theDM-RS may be transmitted without intentionally performing precoding.

The overhead of the time-frequency resource (that is, reference signalRE (subcarrier)) of the DM-RS may be set different depending on therank, that is, the number of transmission layers (or streams).

Two CDM groups (time-frequency resources (RS RE) setting the uniqueorthogonal resources of the reference signal as CDM) may be used forDM-RS. Any CDM group is constituted in the same pattern as afrequency-shifted version of another CDM group. Accordingly, in the caseof rank-1 or rank-2, one CDM group is used and in the case of rank-3 orhigher (up to rank-8), two CDM groups apply to any PRB.

For instance, in the case that the CDM group is defined with twelve RSRE's (that is, subcarriers), at rank-2 or lower, the RS RE overhead is12 and at rank-3 or higher, RS RE overhead is 24. The RS-RE overheadmeans the number of reference signal RE's included in the PRB. If theRS-RE overhead increases, the number of RE's that may be used for datatransmission decreases.

The above description is based on the assumption that the downlink MIMOprecoding applies. Under a certain circumstance where the precoding doesnot apply, RS resources orthogonal while not precoded for each antennaport may apply in association with the number of antenna ports

In any CDM group, the to-be-supported antenna port or RS resource foreach transmission layer may be defined using time domain (that is, overOFDM symbols defined in light RS RE) orthogonal code cover (OCC). Atthis time, in the case that the number of whole ranks is equal to orless than 4, 2 applies to the code length of the OCC and in the casethat the number of the whole ranks is more than 4, the code length ofthe OCC may apply as 4. In the former situation (when the code length is2), this may be equivalently defined as the OCC orthogonal sequencehaving a code length of 4 and may then apply.

FIG. 27 illustrates an example of applying two CDM groups and the OCCapplied for each CDM group.

Referring to FIG. 27, the first CDM group may include RE's marked with Aand B, and the second CDM group may include RE's marked with C and D.Each CDM group has a RS RE overhead of 12. And, the second CDM group isa frequency-shifted version of the first CDM group. As shown in FIG.27A, two sequences having an OCC code length of 2—for example, {1,1},{1,−1}—may apply to each CDM group or two sequences having an OCC codelength of 4—for example, {1,1,1,1}, {1,−1,1,−1}—may apply to each CDMgroup. Or as shown in FIG. 27B, four codes having an OCC code length of4—for example, {1,1,1,1}, {1,−1,1,−1}, {1,1,−1,−1}, {1,−1,−1,1}—mayapply to each CDM group.

Hereinafter, mapping between the layer and antenna port, mapping betweenthe antenna port and reference signal resource, or mapping between thelayer and reference signal resource is described.

In the case that MIMO precoding applies in setting the downlink resourcefor any terminal, as many reference signal resources as the number ofthe transmission layers are set and for each reference signal resource amapping relationship between the resource and antenna port may be set.Or mapping of the transmission layer to the antenna port may beconsidered or as a method of mapping the transmission layer directly toeach of the reference signal resources, mapping the individual DM-RSpattern to the transmission layer may apply. According to these methods,the reference signal resources required depending on the rank value maybe set and operated sequentially from the beginning so that the DM-RSresources set for specific transmission layer may be fixed regardless ofthe rank value.

TABLE 5 DM-RS pattern group Layer index index Code resource index 0 0 01 0 1 2 1 0 3 1 1 4 0 2 5 1 2 6 0 3 7 1 3

In the case that MIMO precoding does not apply in light of settingdownlink resources to any terminal, as many reference signal resourcesas the number of antenna ports set for transmission are set and for eachreference signal resource the antenna ports may be mapped. Or a methodof mapping the individual DM-RS pattern to the individual antenna portmay apply as a method of performing the setting based on a predefinedmapping process. At this time, Table 6 may be referred to in which thelayer index in Table 4 may be replaced with the antenna port index andthe remainder may be used as is. That is, mapping between the antennaport and reference signal resource may be conducted using, as is, themapping method as described in connection with Table 5.

TABLE 6 Antenna port index DM-RS pattern group (or order) index Coderesource index 0 0 0 1 0 1 2 1 0 3 1 1 4 0 2 5 1 2 6 0 3 7 1 3

FIG. 28 is a block diagram illustrating a radio communication systemimplementing the embodiments of the present invention.

The base station 50 includes a processor 51, a memory 53, and a RF(Radio Frequency) unit 52.

The processor 51 implements the suggested functions, processes, and/ormethods. The memory 53 is connected to the processor 51 and storesprotocols or parameters for the multicarrier operation. The RF unit 52is connected to the processor 51 and transmits and/or receives radiosignals.

The relay station 60 includes a processor 61, a memory 62, and an RFunit 63.

The processor 61 implements the suggested functions, procedures, and/ormethods. In the above-described embodiments, the operation of the relaystation may be implemented by the processor 61. That is, the processor61 receives R-PDCCH (Relay-Physical Downlink Control Channel) includingbackhaul control information from the base station and R-PDSCH(Relay-Physical Downlink Shared Channel) including backhaul data fromthe base station. In this case, the R-PDCCH is received in any oneselected from plural predetermined transmission modes and uses thereference signal received through the R-PDCCH for demodulation/decodingof the R-PDCCH. The memory 62 is connected to the processor 61 andstores protocols or parameters for multicarrier operation. The RF unit63 is connected to the processor 61 and transmits and/or receives radiosignals.

The processors 51 and 61 may include ASIC's (Application-SpecificIntegrated Circuits), other chipsets, logic circuits, and/or dataprocessing devices. The memories 53 and 62 may include ROM's (Read-OnlyMemories), RAM's (Random Access Memories), flash memories, memory cards,storage media, and/or other storage devices. The RF units 52 and 63 mayinclude a baseband circuit for processing radio signals. When theembodiments are implemented in software, the above-described schemes maybe configured in modules (procedures, functions, etc.) that perform thefunctions. The modules may be stored in the memories 53 and 62 andexecuted by the processors 51 and 61. The memories 53 and 62 may belocated inside or outside the processors 51 and 61 or may be connectedto the processors 51 and 61 via various known means.

Although in the above-described system the methods are described inflowchart based on a series of steps or blocks, the steps for thepresent invention are not limited to the order of the steps, and a stepmay be performed in order different from another step or simultaneouslywith another step. Or one of ordinary skill may understand that thesteps in the flowchart are not exclusive and other steps may be includedor one or more steps in the flowchart may be omitted without influencingthe scope of the present invention.

The invention has been explained above with reference to exemplaryembodiments. It will be evident to those skilled in the art that variousmodifications may be made thereto without departing from the widerspirit and scope of the invention. Further, although the invention hasbeen described in the context its implementation in particularenvironments and for particular applications, those skilled in the artwill recognize that the present invention's usefulness is not limitedthereto and that the invention can be beneficially utilized in anynumber of environments and implementations. The foregoing descriptionand drawings are, accordingly, to be regarded in an illustrative ratherthan a restrictive sense.

What is claimed is:
 1. A method of transmitting a signal, performed by abase station, the method comprising: transmitting control information,to a relay node, through a relay-physical downlink control channel(R-PDCCH); and transmitting a data, to the relay node, through arelay-physical downlink shared channel (R-PDSCH), wherein when a numberof transmission layers of the R-PDSCH is 2 or more than 2, referencesignals, among a plurality of reference signals, transmitted by aspecific one of a plurality of antenna ports are used, in the relaynode, for a demodulation of the control information.
 2. The method ofclaim 1, wherein a number of the plurality of reference signals used fora demodulation of the data, in the relay node, is same as a number oftransmission layers of the R-PDSCH.
 3. The method of claim 1, wherein anumber of transmission layers of the R-PDCCH is
 1. 4. The method ofclaim 1, wherein the control information and the data are transmitted atdifferent times in a same subframe.
 5. The method of claim 1, whereinthe reference signals used for a demodulation of the control informationhave a minimum index among a plurality of reference signals used for ademodulation of the data in the relay node.
 6. A base station,comprising: a radio frequency (RF) unit configured to transmit andreceive a radio signal; and a processor connected to the RF unit,wherein the processor is configured to: transmit control information, toa relay node, through a relay-physical downlink control channel(R-PDCCH); and transmit a data, to the relay node, through arelay-physical downlink shared channel (R-PDSCH), wherein when a numberof transmission layers of the R-PDSCH is 2 or more than 2, referencesignals, among a plurality of reference signals, transmitted by aspecific one of a plurality of antenna ports are used, in the relaynode, for a demodulation of the control information.
 7. The base stationof claim 6, wherein a number of the plurality of reference signals usedfor a demodulation of the data, in the relay node, is same as a numberof transmission layers of the R-PDSCH.
 8. The base station of claim 6,wherein a number of transmission layers of the R-PDCCH is
 1. 9. The basestation of claim 6, wherein the control information and the data aretransmitted at different times in a same subframe.
 10. The base stationof claim 6, wherein the reference signals used for a demodulation of thecontrol information have a minimum index among a plurality of referencesignals used for a demodulation of the data in the relay node.